AR42J-B-13 cell: an expandable progenitor to generate an unlimited supply of functional hepatocytes

The methylimidazolium ionic liquid M8OI is a substrate for OCT1 and p-glycoprotein-1 in rat

The methylimidazolium ionic liquid M8OI was recently found to be present in both the environment and man. In this study, M8OI disposition and toxicity were examined in an established rat progenitor-hepatocyte model. The progenitor B-13 cell was approx. 13 fold more sensitive to the toxic effects of M8OI than the hepatocyte B-13/H cell. However, this difference in sensitivity was not associated with a difference in metabolic capacities. M8OI toxicity was significantly decreased in a dose-dependent manner by co-addition of the OCT1 (SLC22A1) inhibitor clonidine, but not by OCT2 or OCT3 inhibitors in B-13 cells. M8OI toxicity was also dose-dependently increased by the co-addition of p-glycoprotein-1 (ABCB1B, multi drug resistant protein 1 (MDR1)) substrates/inhibitors. Excretion of B-13-loaded fluorophore Hoechst 33342 was also inhibited by the p-glycoproteins substrate cyclosporin A and by M8OI in a dose-dependent manner. Comparing levels of OCT and p-glycoprotein transcripts and proteins in B-13 and B-13/H cells suggest that the lower sensitivity to M8OI in B-13/H cells is predominantly associated with their higher expression of p-glycoprotein-1. These data together therefore suggest that a determinant in M8OI toxicity in rats is the expression and activity of the p-glycoprotein-1 transporter.

Primary Broiler Hepatocytes for Establishment of a Steatosis Model

Fatty liver hemorrhage syndrome (FLHS) in chickens is characterized by steatosis and bleeding in the liver, which has caused huge losses to the poultry industry. This study aimed to use primary cultured broiler hepatocytes to establish a steatosis model to explore the optimal conditions for inducing steatosis by incubating the cells with a fat emulsion. Primary hepatocytes were isolated from an AA broiler by a modified two-step in situ perfusion method. Hepatocytes were divided into an untreated control group and a fat emulsion group that was incubated with 2.5, 5, 10, or 20% fat emulsion for different times to determine the optimal conditions for inducing steatosis of primary hepatocytes. Incubation of the cells with 10% fat emulsion resulted in cell viability at 48 h of 67%, which was higher than the control group and met the requirements of the model. In the second experiment, steatosis was induced by incubating hepatocytes with 10% fat emulsion for 48 h. In consequence, the apoptosis rate decreased (p > 0.05) and the concentration of ALT (p < 0.001), AST (p < 0.01), and TG (p < 0.05) increased significantly; the expression level of SREBP-1c (p < 0.05) increased, and the expression levels of PPARα (p < 0.001), CPT1 (p < 0.001), and CPT2 (p < 0.05) were lower in the fat emulsion group than in the control group. In conclusion, the induction condition was selected as 10% fat emulsion incubation for 48 h, and we successfully established a fatty liver degeneration model for broilers.

The methylimidazolium ionic liquid M8OI is detectable in human sera and is subject to biliary excretion in perfused human liver

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M8OI was recently found to be contaminating the environment.

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M8OI was detected in the sera from 5/20 PBC patients and 1/10 controls.

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M8OI is taken up by human liver hepatocytes.

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M8OI is sequentially metabolised by CYPs followed by oxidation by dehydrogenases.

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The final carboxylic acid metabolite COOH7IM is, in part, excreted into human bile.

A methylimidizolium ionic liquid (M8OI) was recently found to be contaminating the environment and to be related to and/or potentially a component of an environmental trigger for the autoimmune liver disease primary biliary cholangitis (PBC). The aims of this study were to investigate human exposure to M8OI, hepatic metabolism and excretion. PBC patient and control sera were screened for the presence of M8OI. Human livers were perfused with 50μM M8OI in a closed circuit and its hepatic disposition examined. Metabolism was examined in cultured human hepatocytes and differentiated HepaRG cells by the addition of M8OI and metabolites in the range 10–100 μM. M8OI was detected in the sera from 5/20 PBC patients and 1/10 controls. In perfused livers, M8OI was cleared from the plasma with its appearance – primarily in the form of its hydroxylated (HO8IM) and carboxylated (COOH7IM) products – in the bile. Metabolism was reflected in cultured hepatocytes with HO8IM production inhibited by the cytochrome P450 inhibitor ketoconazole. Further oxidation of HO8IM to COOH7IM was sequentially inhibited by the alcohol and acetaldehyde dehydrogenase inhibitors 4-methyl pyrazole and disulfiram respectively. Hepatocytes from 1 donor failed to metabolise M8OI to COOH7IM over a 24 h period. These results demonstrate exposure to M8OI in the human population, monooxygenation by cytochromes P450 followed by alcohol and acetaldehyde dehydrogenase oxidation to a carboxylic acid that are excreted, in part, via the bile in human liver.

Expression of serine/threonine protein kinase SGK1F promotes an hepatoblast state in stem cells directed to differentiate into hepatocytes

The rat pancreatic AR42J-B13 (B-13) cell line differentiates into non-replicative hepatocyte-like (B-13/H) cells in response to glucocorticoid. Since this response is dependent on an induction of serine/threonine protein kinase 1 (SGK1), this may suggest that a general pivotal role for SGK1 in hepatocyte maturation. To test this hypothesis, the effects of expressing adenoviral-encoded flag tagged human SGK1F (AdV-SGK1F) was examined at 3 stages of human induced pluripotent stem cell (iPSC) differentiation to hepatocytes. B-13 cells infected with AdV-SGK1F in the absence of glucocorticoid resulted in expression of flag tagged SGK1F protein; increases in β-catenin phosphorylation; decreases in Tcf/Lef transcriptional activity; expression of hepatocyte marker genes and conversion of B-13 cells to a cell phenotype near-similar to B-13/H cells. Given this demonstration of functionality, iPSCs directed to differentiate towards hepatocyte-like cells using a standard protocol of chemical inhibitors and mixtures of growth factors were additionally infected with AdV-SGK1F, either at an early time point during differentiation to endoderm; during endoderm differentiation to anterior definitive endoderm and hepatoblasts and once converted to hepatocyte-like cells. SGK1F expression had no effect on differentiation to endoderm, likely due to low levels of expression. However, expression of SGK1F in both iPSCs-derived endoderm and hepatocyte-like cells both resulted in promotion of cells to an hepatoblast phenotype. These data demonstrate that SGK1 expression promotes an hepatoblast phenotype rather than maturation of human iPSC towards a mature hepatocyte phenotype and suggest a transient role for Sgk1 in promoting an hepatoblast state in B-13 trans-differentiation to B-13/H cells.

Stem Cell-Based Therapies for Liver Diseases: An Overview and Update

BACKGROUND

Liver disease is one of the top causes of death globally. Although liver transplantation is a very effective treatment strategy, the shortage of available donor organs, waiting list mortality, and high costs of surgery remain huge problems. Stem cells are undifferentiated cells that can differentiate into a variety of cell types. Scientists are exploring the possibilities of generating hepatocytes from stem cells as an alternative for the treatment of liver diseases.

METHODS

In this review, we summarized the updated researches in the field of stem cell-based therapies for liver diseases as well as the current challenges and future expectations for a successful cell-based liver therapy.

RESULTS

Several cell types have been investigated for liver regeneration, such as embryonic stem cells, induced pluripotent stem cells, liver stem cells, mesenchymal stem cells, and hematopoietic stem cells. In vitro and in vivo studies have demonstrated that stem cells are promising cell sources for the liver regeneration.

CONCLUSION

Stem cell-based therapy could be a promising therapeutic method for patients with end-stage liver disease, which may alleviate the need for liver transplantation in the future.

Next generation in vitro liver model design: Combining a permeable polystyrene membrane with a transdifferentiated cell line

Herein we describe the manufacture and characterisation of biocompatible, porous polystyrene membranes, suitable for cell culture. Though widely used in traditional cell culture, polystyrene has not been used as a hollow fibre membrane due to its hydrophobicity and non-porous structure. Here, we use microcrystalline sodium chloride (4.7 ± 1.3 µm) to control the porosity of polystyrene membranes and oxygen plasma surface treatment to reduce hydrophobicity. Increased porogen concentration correlates to increased surface pore density, macrovoid formation, gas permeability and mean pore size, but a decrease in mechanical strength. For tissue engineering applications, membranes spun from casting solutions containing 40% (w/w) sodium chloride represent a compromise between strength and permeability, having surface pore density of 208.2 ± 29.7 pores/mm², mean surface pore size of 2.3 ± 0.7 µm, and Young's modulus of 115.0 ± 8.2 MPa. We demonstrate the biocompatibility of the material with an exciting cell line-media combination: transdifferentiation of the AR42J-B13 pancreatic cell line to hepatocyte-like cells. Treatment of AR42J-B13 with dexamethasone/oncostatin-M over 14 days induces transdifferentiation towards a hepatic phenotype. There was a distinct loss of the pancreatic phenotype, shown through loss of expression of the pancreatic marker amylase, and gain of the hepatic phenotype, shown through induction of expression of the hepatic markers transferrin, carbamoylphosphate synthetase and glutamine synthetase. The combination of this membrane fabrication method and demonstration of biocompatibility of the transdifferentiated hepatocytes provides a novel, superior, alternative design for in vitro liver models and bioartificial liver devices.

Glucocorticoid-induced pancreatic-hepatic trans-differentiation in a human cell line in vitro

The rodent pancreatic AR42J-B13 (B-13) cell line differentiates into non-replicative hepatocyte-like cells in response to glucocorticoid mediated via the glucocorticoid receptor (GR). The aims of this study were to identify a human cell line that responds similarly and investigate the mechanisms underpinning any alteration in differentiation. Exposing the human pancreatic adenocarcinoma (HPAC) cell line to 1-10 µM concentrations of dexamethasone (DEX) resulted an inhibition of proliferation, suppressed carcinoembryonic antigen expression, limited expression of pancreatic acinar and hepatic gene expression and significant induction of the constitutively-expressed hepatic CYP3A5 mRNA transcript. These changes were associated with a pulse of genomic DNA methylation and suppressed notch signalling activity. HPAC cells expressed high levels of GR transcript in contrast to other nuclear receptors - such as the glucocorticoid-activated pregnane X receptor (PXR) - and GR transcriptional function was activated by DEX in HPAC cells. Expression of selected hepatocyte transcripts in response to DEX was blocked by co-treatment with the GR antagonist RU486. These data indicate that the HPAC response to glucocorticoid exposure includes an inhibition in proliferation, alterations in notch signalling and a limited change in the expression of genes associated with an acinar and hepatic phenotype. This is the first demonstration of a human cell responding to similarly to the rodent B-13 cell regarding formation of hepatocyte-like cells in response to glucocorticoid. Identifying and modulating the ablating factor(s) may enhance the hepatocyte-like forming capacity of HPAC cells after exposure to glucocorticoid and generate an unlimited in vitro supply of human hepatocytes for toxicology studies and a variety of clinical applications.

Transdifferentiation of pancreatic progenitor cells to hepatocyte-like cells is not serum-dependent when facilitated by extracellular matrix proteins

The rising prevalence of chronic liver disease, coupled with a permanent shortage of organs for liver transplantation, has sparked enormous interest in alternative treatment strategies. Previous protocols to generate hepatocyte-like cells (HLCs) via pancreas-to-liver transdifferentiation have utilised fetal bovine serum, introducing unknown variables and severely limiting study reproducibility. Therefore, the main goal of this study was to develop a protocol for transdifferentiation of pancreatic progenitor cells to HLCs in a chemically defined, serum-free culture medium. The clonal pancreatic progenitor cell line AR42J-B13 was cultured in basal growth medium on uncoated plastic culture dishes in the absence or presence of Dexamethasone on uncoated, laminin- or fibronectin-coated culture substrata, with or without serum supplementation. The hepatocytic differentiation potential was evaluated: (i) morphologically through bright-field and scanning electron microscopy, (ii) by assessing pancreatic and hepatic marker expression and (iii) by determining the function of HLCs through their ability to synthesise glycogen or take up and release indocyanine green. Here we demonstrate for the first time that transdifferentiation of pancreatic cells to HLCs is not dependent on serum. These results will assist in converting current differentiation protocols into procedures that are compliant with clinical use in future cell-based therapies to treat liver-related metabolic disorders.

B-13 progenitor-derived hepatocytes (B-13/H cells) model lipid dysregulation in response to drugs and chemicals

Lipid dysregulation is a common hepatic adverse outcome after exposure to toxic drugs and chemicals. A donor-free rat hepatocyte-like (B-13/H) cell was therefore examined as an in vitro model for investigating mechanisms. The B-13/H cell irreversibly accumulated triglycerides (steatosis) in a time- and dose-dependent manner when exposed to fatty acids, an effect that was potentiated by the combined addition of hyperglycaemic levels of glucose and insulin. B-13/H cells also expressed the LXR nuclear receptors and exposure to their activators – T0901317 or GW3965 – induced luciferase expression from a transfected LXR-regulated reporter gene construct and steatosis in a dose-dependent manner with T0901317. Exposing B-13/H cells to a variety of cationic amphiphilic drugs – but not other hepatotoxins – also resulted in a time- and dose-dependent accumulation of phospholipids (phospholipidosis), an effect that was reduced by over-expression of lysosomal phospholipase A2. Through application of this model, hepatotoxin methapyrilene exposure was shown to induce phospholipidosis in both B-13 and B-13/H cells in a time- and dose-dependent manner. However, methapyrilene was only toxic to B-13/H cells and inhibitors of hepatotoxicity enhanced phospholipidosis, suggesting phospholipidosis is not a pathway in toxicity for this withdrawn drug. In contrast, pre-existing steatosis had minimal effect on methapyrilene hepatotoxicity in B-13/H cells. These data demonstrate that the donor free B-13 cell system for generating hepatocyte-like cells may be employed in studies of fatty acid- and LXR activator-induced steatosis and phospholipidosis and in the dissection of pathways leading to adverse outcomes such as hepatotoxicity.

Cell sources for in vitro human liver cell culture models

In vitro liver cell culture models are gaining increasing importance in pharmacological and toxicological research. The source of cells used is critical for the relevance and the predictive value of such models. Primary human hepatocytes (PHH) are currently considered to be the gold standard for hepatic in vitro culture models, since they directly reflect the specific metabolism and functionality of the human liver; however, the scarcity and difficult logistics of PHH have driven researchers to explore alternative cell sources, including liver cell lines and pluripotent stem cells. Liver cell lines generated from hepatomas or by genetic manipulation are widely used due to their good availability, but they are generally altered in certain metabolic functions. For the past few years, adult and pluripotent stem cells have been attracting increasing attention, due their ability to proliferate and to differentiate into hepatocyte-like cells in vitro However, controlling the differentiation of these cells is still a challenge. This review gives an overview of the major human cell sources under investigation for in vitro liver cell culture models, including primary human liver cells, liver cell lines, and stem cells. The promises and challenges of different cell types are discussed with a focus on the complex 2D and 3D culture approaches under investigation for improving liver cell functionality in vitro Finally, the specific application options of individual cell sources in pharmacological research or disease modeling are described.

Pancreatic B-13 Cell Trans-Differentiation to Hepatocytes Is Dependent on Epigenetic-Regulated Changes in Gene Expression

The proliferative B-13 pancreatic cell line is unique in its ability to generate functional hepatocyte-like (B-13/H) cells in response to exposure to glucocorticoid. In these studies, quantitatively comparable hepatic levels of liver-specific and liver-enriched transcription factor and hepatocyte defining mRNA transcripts were expressed after 10–14 days continuous treatment with glucocorticoid. This conversion in phenotype was associated with increased Gr-α mRNA expression and translation of a functional N-terminally truncated variant protein that localized to the nucleus in B-13/H cells. A short (6 hours) pulse exposure to glucocorticoid was also sufficient to transiently activate the Gr and irreversibly drive near identical conversion to B-13/H cells. Examination of epigenetic-related mechanisms demonstrated that B-13 DNA was rapidly methylated and de-methylated over the initial 2 days in response to both continuous or pulse exposure with glucocorticoid. DNA methylation and glucocorticoid-dependent conversion to an hepatic B-13/H phenotype was blocked by the methylation inhibitor, 5-azacytidine. Conversion to an hepatic B-13/H phenotype was also blocked by histone deacetylase inhibitors. Previous experiments have identified N-terminal Sgk1 variant proteins as pivotal to the mechanism(s) associated with pancreatic–hepatic differentiation. Both continuous and pulse exposure to DEX was sufficient to result in a near-similar robust transcriptional increase in Sgk1c mRNA expression from undetectable levels in B-13 cells. Notably, expression of Sgk1c mRNA remained constitutive 14 days later; including after pulse exposure to glucocorticoid and this induction was inhibited by 5-azacytidine or by histone deacetylase inhibitors. These data therefore suggest that exposing B-13 cells to glucocorticoid results in a Gr-dependent pulse in DNA methylation and likely other epigenetic changes such as histone modifications that leads to constitutive expression of Sgk1c and irreversible reprogramming of B-13 cells into B-13/H cells. Understanding and application of these mechanism(s) may enhance the functionality of stem cell-derived hepatocytes generated in vitro.

Pancreatic progenitor-derived hepatocytes are viable and functional in a 3D high density bioreactor culture system

The rat pancreatic progenitor cell line B-13 is of interest for research on drug metabolism and toxicity since the cells trans-differentiate into functional hepatocyte-like cells (B-13/H) when treated with glucocorticoids. In this study we investigated the trans-differentiation and liver-specific functions of B-13/H cells in a three-dimensional (3D) multi-compartment bioreactor, which has already been successfully used for primary liver cell culture. Undifferentiated B-13 cells were inoculated into the bioreactor system and exposed to dexamethasone to promote hepatic trans-differentiation (B-13/HT). In a second approach, pre-differentiated B-13 cells were cultured in bioreactors for 15 days to evaluate the maintenance of liver-typical functions (B-13/HP). During trans-differentiation of B-13 cells into hepatocyte-like cells in the 3D bioreactor system (approach B-13/HT), an increase in glucose metabolism and in liver-specific functions (urea and albumin synthesis; cytochrome P450 [CYP] enzyme activity) was observed, whereas amylase - characteristic for exocrine pancreas and undifferentiated B-13 cells - decreased over time. In bioreactors with pre-differentiated cells (approach B-13/HP), the above liver-specific functions were maintained over the whole culture period. Results were confirmed by gene expression and protein analysis showing increased expression of carbamoyl-phosphate synthase 1 (CPS-1), albumin, CYP2E1, CYP2C11 and CYP3A1 with simultaneous loss of amylase. Immunohistochemical studies showed the formation of 3D structures with expression of liver-specific markers, including albumin, cytokeratin (CK) 18, CCAAT/enhancer-binding protein beta (CEBP-β), CYP2E1 and multidrug resistance protein 2 (MRP2). In conclusion, successful culture and trans-differentiation of B-13 cells in the 3D bioreactor was demonstrated. The requirement for only one hormone and simple culture conditions to generate liver-like cells makes this cell type useful for in vitro research using 3D high-density culture systems.

Progenitor-derived hepatocyte-like (B-13/H) cells metabolise 1'-hydroxyestragole to a genotoxic species via a SULT2B1-dependent mechanism

Rat B-13 progenitor cells are readily converted into functional hepatocyte-like B-13/H cells capable of phase I cytochrome P450-dependent activation of pro-carcinogens and induction of DNA damage. The aim of the present study was to investigate whether the cells are also capable of Phase II sulphotransferase (SULT)-dependent activation of a pro-carcinogen to an ultimate carcinogen. To this end we therefore examined the bioactivation of the model hepatic (hepato- and cholangio-) carcinogen estragole and its proximate SULT1A1-activated genotoxic metabolite 1'-hydroxyestragole. Exposing B-13 or B-13/H cells to estragole (at concentrations up to 1mM) resulted in the production of low levels of 1'-hydroxyestragole, but did not result in detectable DNA damage. Exposing B-13/H cells - but not B-13 cells - to 1'-hydroxyestragole resulted in a dose-dependent increase in DNA damage in comet assays, confirmed by detection of N(2)-(trans-isoestragol-3'-yl)-2'-deoxyguanosine adducts. Genotoxicity was inhibited by general SULT inhibitors, supporting a role for SULTS in the activation of 1-hydroxyestragole in B-13/H cells. However, B-13 and B-13/H cells did not express biologically significant levels of SULT1A1 as determined by qRT-PCR, Western blotting and its associated 7-hydroxycoumarin sulphation activity. B-13 and B-13/H cells expressed - relative to intact rat liver - high levels of SULT2B1 (primarily the b isoform) and SULT4A1 mRNAs and proteins. B-13 and B-13/H cells also expressed the 3'-phosphoadenosine 5'-phosphosulphate synthase 1 required for the generation of activated sulphate cofactor 3'-phosphoadenosine 5'-phosphosulphate. However, only B-13/H cells expressed functional SULT activities towards SULT2B1 substrates DHEA, pregnenolone and 4 methylumbelliferone. Since liver progenitor cells are bi-potential and also form cholangiocytes, we therefore hypothesised that B-13 cells express a cholangiocyte-like SULT profile. To test this hypothesis, the expression of SULTs was examined in liver by RT-PCR and immunohistochemistry. SULT2B1 - but not SULT1A1 - was determined to be expressed in both rat and human cholangiocytes. Since 1'-hydroxyestragole exposure readily produced DNA injury in B-13/H cells, these data suggest that cholangiocarcinomas generated in rats fed estragole may be dependent, in part, on SULT2B1 activation of the 1'-hydroxyestragole metabolite.

Acinar cell reprogramming: a clinically important target in pancreatic disease

Acinar cells of the pancreas produce the majority of enzymes required for digestion and make up >90% of the cells within the pancreas. Due to a common developmental origin and the plastic nature of the acinar cell phenotype, these cells have been identified as a possible source of β cells as a therapeutic option for Type I diabetes. However, recent evidence indicates that acinar cells are the main source of pancreatic intraepithelial neoplasias (PanINs), the predecessor of pancreatic ductal adenocarcinoma (PDAC). The conversion of acinar cells to either β cells or precursors to PDAC is dependent on reprogramming of the cells to a more primitive, progenitor-like phenotype, which involves changes in transcription factor expression and activity, and changes in their epigenetic program. This review will focus on the mechanisms that promote acinar cell reprogramming, as well as the factors that may affect these mechanisms.

Metabolic phenotype-microRNA data fusion analysis of the systemic consequences of Roux-en-Y gastric bypass surgery

Background/Objectives:

Bariatric surgery offers sustained marked weight loss and often remission of type 2 diabetes, yet the mechanisms of establishment of these health benefits are not clear.

Subjects/Methods:

We mapped the coordinated systemic responses of gut hormones, the circulating miRNAome and the metabolome in a rat model of Roux-en-Y gastric bypass (RYGB) surgery.

Results:

The response of circulating microRNAs (miRNAs) to RYGB was striking and selective. Analysis of 14 significantly altered circulating miRNAs within a pathway context was suggestive of modulation of signaling pathways including G protein signaling, neurodegeneration, inflammation, and growth and apoptosis responses. Concomitant alterations in the metabolome indicated increased glucose transport, accelerated glycolysis and inhibited gluconeogenesis in the liver. Of particular significance, we show significantly decreased circulating miRNA-122 levels and a more modest decline in hepatic levels, following surgery. In mechanistic studies, manipulation of miRNA-122 levels in a cell model induced changes in the activity of key enzymes involved in hepatic energy metabolism, glucose transport, glycolysis, tricarboxylic acid cycle, pentose phosphate shunt, fatty-acid oxidation and gluconeogenesis, consistent with the findings of the in vivo surgery-mediated responses, indicating the powerful homeostatic activity of the miRNAs.

Conclusions:

The close association between energy metabolism, neuronal signaling and gut microbial metabolites derived from the circulating miRNA, plasma, urine and liver metabolite and gut hormone correlations further supports an enhanced gut-brain signaling, which we suggest is hormonally mediated by both traditional gut hormones and miRNAs. This transomic approach to map the crosstalk between the circulating miRNAome and metabolome offers opportunities to understand complex systems biology within a disease and interventional treatment setting.

An expandable donor-free supply of functional hepatocytes for toxicology

The B-13 cell is a readily expandable rat pancreatic acinar-like cell that differentiates on simple plastic culture substrata into replicatively-senescent hepatocyte-like (B-13/H) cells in response to glucocorticoid exposure. B-13/H cells express a variety of liver-enriched and liver-specific genes, many at levels similar to hepatocytes in vivo. Furthermore, the B-13/H phenotype is maintained for at least several weeks in vitro, in contrast to normal hepatocytes which rapidly de-differentiate under the same simple – or even under more complex – culture conditions. The origin of the B-13 cell line and the current state of knowledge regarding differentiation to B-13/H cells are presented, followed by a review of recent advances in the use of B-13/H cells in a variety of toxicity endpoints. B-13 cells therefore offer Toxicologists a cost-effective and easy to use system to study a range of toxicologically-related questions. Dissecting the mechanism(s) regulating the formation of B-13/H cell may also increase the likelihood of engineering a human equivalent, providing Toxicologists with an expandable donor-free supply of functional rat and human hepatocytes, invaluable additions to the tool kit of in vitro toxicity tests.

Utility of B-13 progenitor-derived hepatocytes in hepatotoxicity and genotoxicity studies

AR42J-B-13 (B-13) cells form hepatocyte-like (B-13/H) cells in response to glucocorticoid treatment. To establish its utility in toxicity and genotoxicity screening, cytochrome P450 (CYP) induction, susceptibility to toxins, and transporter gene expression were examined. Conversion to B-13/H cells resulted in expression of male-specific CYP2C11 and sensitivity to methapyrilene. B-13/H cells constitutively expressed CYP1A, induced expression in response to an aryl hydrocarbon receptor agonist, and activated benzo[α]pyrene to a DNA-damaging species. Functional CYP1A2 was not expressed due to deletions in the Cyp1a2 gene. A B-13 cell line stably expressing the human CYP1A2 was therefore engineered (B-13^−TR/h1A2) and the derived B-13/H cells expressed metabolically functional CYP1A2. Treatment with the cooked food mutagen 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine resulted in a dose-dependent increase in DNA damage. B-13/H cells expressed constitutive androstane receptor (CAR) and induced CYP2B1 mRNA levels in response to classical CAR activators. However, translation to functional CYP2B1 protein was low and increased minimally by CAR activator treatment. B-13/H cells expressed high levels of pregnane X-receptor (PXR) and induced CYP3A1 in response to classical PXR activators. CYP3A genes were inducible, functional, and activated aflatoxin B1 to a DNA-damaging species. All 23 major hepatic transporters were induced when B-13 cells were converted to B-13/H cells, although in many cases, levels remained below those present in adult rat liver. However, bile salt export pump, Abcb1b, multidrug resistance-associated protein, and breast cancer resistance protein transporters were functional in B-13/H cells. These data demonstrate that the B-13 cell generates hepatocyte-like cells with functional drug metabolism and transporter activities, which can alone—or in a humanized form—be used to screen for hepatotoxic and genotoxic endpoints in vitro.

Efficient differentiation of AR42J cells towards insulin-producing cells using pancreatic transcription factors in combination with growth factors

The AR42J-B13 rat pancreatic acinar cell line was used to identify pancreatic transcription factors and exogenous growth factors (GFs) that might facilitate the reprogramming of exocrine cells into islets. Adenoviruses were used to induce exogenous expression of the pancreatic transcription factors (TFs) Pdx1, MafA, Ngn3 and Pax4. Individually Pdx1, MafA and Pax4 had no effect on the expression of endocrine markers, whilst adeno-Ngn3 on its own increased the expression of Pax4, Ngn3 and NeuroD. In combination the four TFs had a significant effect on the expression of insulin 1 and 2 that was associated with a change in cell morphology from a rounded to a spindle-like shape. Amongst a range of growth factors, Betacellulin and Nicotinamide were shown to enhance the effects of the four TFs. The presence of adeno-Pax4 in the differentiation cocktail was important in limiting the expression of glucagon and in generating glucose sensitive insulin secretion. Further experiments asked whether the adenoviral TFs could be replaced by protein transduction domain (PTD)-containing TFs. The results showed that the PTD-TFs could mimic in part the effects of the adeno-TFs, but the resultant cells did not undergo the important morphological change associated with differentiation to endocrine lineages and levels of endogenous markers were very much lower. In summary, the results describe a cocktail of four TFs and two GFs that can be used to induce formation of glucose sensitive insulin secreting cells from ARJ42 cells, and demonstrate that it would be difficult to replace adenoviral transduction with PTD-TFS.

A rapid two-step method for isolation of functional primary mouse hepatocytes: cell characterization and asialoglycoprotein receptor based assay development

Primary mouse hepatocytes are an important tool in the biomedical research field for the assessment of hepatocyte function. Several methods for hepatocyte isolation have been published; however, many of these methods require extensive handling and can therefore compromise the viability and function of the isolated cells. Since one advantage of utilizing freshly isolated cells is to maintain an environment in which the cells are more comparable to their in vivo state, it is important to have robust methods that produce cells with high viability, good purity and that function in a similar manner to that in their in vivo state. Here we describe a modified two-step method for the rapid isolation and characterization of mouse primary hepatocytes that results in high yields of viable cells. The asialoglycoprotein receptor (ASGPR), which is one of the most abundant cell surface receptors on hepatocytes, was used to monitor the function of the isolated hepatocytes by demonstrating specific binding of its ligand using a newly developed flow cytometry based ligand-receptor binding assay. Also, an in vitro screening method for siRNA drug candidates was successfully developed utilizing freshly isolated hepatocytes with minimum culture time.

Serine/threonine protein kinase SGK1 in glucocorticoid-dependent transdifferentiation of pancreatic acinar cells to hepatocytes

Elevated glucocorticoid levels result in the transdifferentiation of pancreatic acinar cells into hepatocytes through a process that requires a transient repression of WNT signalling upstream of the induction of C/EBP-β. However, the mechanism by which glucocorticoid interacts with WNT signalling is unknown. A screen of microarray data showed that the serine/threonine protein kinase SGK1 (serum- and glucocorticoid-regulated kinase 1) was markedly induced in the model B-13 pancreatic rat acinar cell line after glucocorticoid treatment (which converts them into hepatocyte-like 'B-13/H' cells) and this was confirmed at the level of mRNA (notably an alternatively transcribed SGK1C form) and protein. Knockdown of SGK1 using an siRNA designed to target all variant transcripts inhibited glucocorticoid-dependent transdifferentiation, whereas overexpression of the human C isoform (and also the human SGK1F isoform, for which no orthologue in the rat has been identified) alone - but not the wild-type A form - inhibited distal WNT signalling Tcf/Lef transcription factor activity, and converted B-13 cells into B-13/H cells. These effects were lost when the kinase functions of SGK1C and SGK1F were mutated. Inhibition of SGK1 kinase activity also inhibited glucocorticoid-dependent transdifferentiation. Expression of SGK1C and SGK1F resulted in the appearance of phosphorylated β-catenin, and recombinant SGK1 was shown to directly phosphorylate purified β-catenin in vitro in an ATP-dependent reaction. These data therefore demonstrate a crucial role for SGK1 induction in B-13 cell transdifferentiation to B-13/H hepatocytes and suggest that direct phosphorylation of β-catenin by SGK1C represents the mechanism of crosstalk between glucocorticoid and WNT signalling pathways.