Collagen type I gel cultures of adult rat hepatocytes as a screening induction model for cytochrome P450-dependent enzymes

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.

Rat primary hepatocytes show enhanced performance and sensitivity to acetaminophen during three-dimensional culture on a polystyrene scaffold designed for routine use

The in vitro evaluation of hepatotoxicity is an essential stage in the research and development of new pharmaceuticals as the liver is one of the most commonly impacted organs during preclinical toxicity studies. Fresh primary hepatocytes in monolayer culture are the most commonly used in vitro model of the liver but often exhibit limited viability and/or reduction or loss of important liver-specific functions. These limitations could potentially be overcome using three-dimensional (3D) culture systems, but their experimental nature and limited use in liver toxicity screening and drug metabolism has impaired their uptake into commercial screening programs. In this study we use a commercially available polystyrene scaffold developed for routine 3D cell culture to maintain primary rat hepatocytes for use in metabolism and toxicity studies over 72 h. We show that primary hepatocytes retain their natural cuboidal morphology with significantly higher viability (>74%) than cells grown in monolayer culture (maximum of 57%). Hepatocytes in the 3D scaffolds exhibit differential expression of genes associated with phase I, II, and III drug metabolism under basal conditions compared with monolayer culture and can be induced to stably express significantly higher levels of the cytochrome-P450 enzymes 1A2, 2B1, and 3A2 over 48 h. In toxicity studies the hepatocytes in the 3D scaffolds also show increased sensitivity to the model toxicant acetaminophen. These improvements over monolayer culture and the availability of this new easy to use 3D scaffold system could facilitate the uptake of 3D technologies into routine drug screening programs.

A sandwich-cultured rat hepatocyte system with increased metabolic competence evaluated by gene expression profiling

A rapid decline of cytochrome P450 (CYP450) enzyme activities remains a drawback of rat hepatocyte-based in vitro cultures. Consequently, judgment of the toxic potential of compounds that need bioactivation by CYP450s may not be adequate using this model. In the present study, an improved hepatocyte-based in vitro system was developed with special focus on metabolic competence. Therefore, a mixture of CYP450 inducers, phenobarbital, dexamethasone and beta-naphthoflavone, was added to culture medium of sandwich-cultured rat hepatocytes. The resulting modified model was evaluated by comparing its genome-wide expression profiles with liver and a standard model without the inducer mixture. Metabolic capacity for CYP450 enzymes showed that the modified model resembled more closely the in vivo situation. Gene expression results revealed large differences between in vivo and both in vitro models. The slight differences between the two sandwich models were predominantly represented by gene expression changes in CYP450s. Importantly, in the modified model, expression ratios of the phase I and the majority of phase II genes more closely resembled liver in vivo. The CYP450 enzyme activities corresponded with gene expression data. In conclusion, for toxicological applications using sandwich-cultured hepatocytes, the modified model may be preferred.

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.

Sequential exposure to cytokines reflecting embryogenesis: the key for in vitro differentiation of adult bone marrow stem cells into functional hepatocyte-like cells

Differentiation of adult bone marrow stem cells (BMSC) into hepatocyte-like cells is commonly performed by continuous exposure to a cytokines-cocktail. Here, it is shown that the differentiation efficacy in vitro can be considerably enhanced by sequential addition of liver-specific factors (fibroblast growth factor-4, hepatocyte growth factor, insulin-transferrin-sodium selenite, and dexamethasone) in a time-dependent order that closely resembles the secretion pattern during in vivo liver embryogenesis. Quantitative RT-PCR analysis and immunocytochemistry showed that, upon sequential exposure to liver-specific factors, different stages of hepatocyte differentiation, as seen during liver embryogenesis, can be mimicked. Indeed, expression of the early hepatocyte markers alpha-fetoprotein and hepatocyte nuclear factor (HNF)3beta decreased as differentiation progressed, whereas levels of the late liver-specific markers albumin (ALB), cytokeratin (CK)18, and HNF1alpha were gradually upregulated. In contrast, cocktail treatment did not significantly alter the expression pattern of the hepatic markers. Moreover, sequentially exposed cells featured highly differentiated hepatic functions, including ALB secretion, glycogen storage, urea production, and inducible cytochrome P450-dependent activity, far more efficiently compared to the cocktail condition. In conclusion, sequential induction of the differentiation process, analogous to in vivo liver development, is crucial for in vitro differentiation of adult rat BMSC into functional hepatocyte-like cells. This model may not only be applicable for in vitro studies of endoderm differentiation but it also provides a "virtually unlimited" source of functional hepatocytes, suitable for preclinical pharmacological research and testing, and cell and organ development.

Effect of culture conditions on the expression and function of Bsep, Mrp2, and Mdr1a/b in sandwich-cultured rat hepatocytes

Rat hepatocytes cultured in a sandwich configuration form functional canalicular networks. The influence of extracellular matrix configuration, medium composition, and confluency on the expression and function of Bsep, Mrp2, and Mdr1a/b in sandwich-cultured (SC) rat hepatocytes was examined. Primary rat hepatocytes were: (1) maintained in various extracellular matrix sandwich configurations, (2) cultured in Dulbecco's modified Eagle's medium (DMEM), Modified Chee's medium (MCM) or Williams' E medium (WME), and/or (3) plated at decreasing cell density. Bsep, Mrp2, and Mrdr1a/b expression in day 4 SC rat hepatocytes was assessed by Western blot; function was measured by accumulation of taurocholate, 5(and 6)-carboxy-2',7'-dichlorofluorescein, and rhodamine 123, respectively, in canalicular networks. In general, the extracellular matrix conditions examined resulted in similar protein expression and function. Function of Bsep, Mrp2, and Mdr1a/b was higher in SC rat hepatocytes maintained in DMEM or WME. Mrp2 and Mdr1a/b expression, representative of total cellular content, did not always correlate directly with function, which should be reflective of canalicular membrane expression. Mrp2 expression decreased significantly as cell density decreased in SC hepatocytes. Low plating density in Biocoat plates resulted in poor canalicular network formation and reduced function of Mrp2 and Mdr1a/b. Expression and/or function of Mrp2 and Mdr1a/b in rat hepatocytes cultured in a sandwich configuration may be influenced by plating density and media type.

Effect of the histone deacetylase inhibitor trichostatin A on spontaneous apoptosis in various types of adult rat hepatocyte cultures

Acetylation and deacetylation of histones, catalysed by histone acetyl transferases and histone deacetylases (HDAC), respectively, are known to be involved in gene expression regulation. Here, the effect on the activity and expression of several apoptosis-related proteins of trichostatin A (TSA), a well-known HDAC inhibitor, were studied in short-term (conventional monolayer) and long-term cultured (collagen I gel sandwich cultures and co-cultures) adult rat hepatocytes. No significant effects of TSA on the caspase-3-like activity were seen in rat hepatocytes cultured in a sandwich configuration or in a co-culture with rat liver epithelial cells of primitive biliary origin. In both culture models, the basal level of apoptosis was found to be much lower than in control monolayer cultures. In the latter system, it was found that, after 4 days of culture, TSA decreased the levels of caspase-3 (both proform and p17 fragment) and of the pro-apoptotic protein Bid. No effect of TSA was found on the expression of Bax. As expected, a TSA-mediated increase of acetylated histones H3 and H4 was observed in all culture systems examined. In addition, in the presence of TSA, increased albumin secretion and cytochrome P450 1A1/2 and 2B1-dependent enzyme activities were found in conventional cultures after 7 days. In conclusion, TSA delayed the occurrence of apoptosis and loss of liver specific functions in conventional hepatocyte monolayers. In contrast, in hepatocyte culture models in which spontaneous apoptosis is already minimised through the addition of either extracellular matrix components (sandwich cultures) or non-parenchymal liver cells (co-cultures), TSA did not have any additional anti-apoptotic effect.