Prolonged maintenance of active cytochrome P-450 in adult rat hepatocytes co-cultured with another liver cell type

Engineering a perfusable 3D human liver platform from iPS cells

In vitro models of human tissue are crucial to our ability to study human disease as well as develop safe and effective drug therapies. Models of single organs in static and microfluidic culture have been established and shown utility for modeling some aspects of health and disease; however, these systems lack multi-organ interactions that are critical to some aspects of drug metabolism and toxicity. Thus, as part of a consortium of researchers, we have developed a liver chip that meets the following criteria: (1) employs human iPS cells from a patient of interest, (2) cultures cells in perfusable 3D organoids, and (3) is robust to variations in perfusion rate so as to be compatible in series with other specialized tissue chips (e.g. heart, lung). In order to achieve this, we describe methods to form hepatocyte aggregates from primary and iPS-derived cells, alone and in co-culture with support cells. This necessitated a novel culture protocol for the interrupted differentiation of iPS cells that permits their removal from a plated surface and aggregation while maintaining phenotypic hepatic functions. In order to incorporate these 3D aggregates in a perfusable platform, we next encapsulated the cells in a PEG hydrogel to prevent aggregation and overgrowth once on chip. We adapted a C-trap chip architecture from the literature that enabled robust loading with encapsulated organoids and culture over a range of flow rates. Finally, we characterize the liver functions of this iHep organoid chip under perfusion and demonstrate a lifetime of at least 28 days. We envision that such this strategy can be generalized to other microfluidic tissue models and provides an opportunity to query patient-specific liver responses in vitro.

Cell sources, liver support systems and liver tissue engineering: alternatives to liver transplantation

The liver is the largest organ in the body; it has a complex architecture, wide range of functions and unique regenerative capacity. The growing incidence of liver diseases worldwide requires increased numbers of liver transplant and leads to an ongoing shortage of donor livers. To meet the huge demand, various alternative approaches are being investigated including, hepatic cell transplantation, artificial devices and bioprinting of the organ itself. Adult hepatocytes are the preferred cell sources, but they have limited availability, are difficult to isolate, propagate poor and undergo rapid functional deterioration in vitro. There have been efforts to overcome these drawbacks; by improving culture condition for hepatocytes, providing adequate extracellular matrix, co-culturing with extra-parenchymal cells and identifying other cell sources. Differentiation of human stem cells to hepatocytes has become a major interest in the field of stem cell research and has progressed greatly. At the same time, use of decellularized organ matrices and 3 D printing are emerging cutting-edge technologies for tissue engineering, opening up new paths for liver regenerative medicine. This review provides a compact summary of the issues, and the locations of liver support systems and tissue engineering, with an emphasis on reproducible and useful sources of hepatocytes including various candidates formed by differentiation from stem cells.

Establishment and characterization of an immortalized human hepatic stellate cell line for applications in co-culturing with immortalized human hepatocytes

BACKGROUND AND OBJECTIVE

The liver-specific functions of hepatocytes are improved by co-culturing hepatocytes with primary hepatic stellate cells (HSC). However, primary HSC have a short lifespan in vitro, which is considered a major limitation for their use in various applications. This study aimed to establish immortalized human HSC using the simian virus 40 large T antigen (SV40LT) for applications in co-culturing with hepatocytes and HSC in vitro.

METHODS

Primary human HSC were transfected with a recombinant retrovirus containing SV40LT. The immortalized human HSC were characterized by analyzing their gene expression and functional characteristics. The liver-specific functions of hepatocytes were evaluated in a co-culture system incorporating immortalized human hepatocytes with HSC-Li cells.

RESULTS

The immortalized HSC line, HSC-Li, was obtained after infection with a recombinant retrovirus containing SV40LT. The HSC-Li cells were longitudinally spindle-like and had numerous fat droplets in their cytoplasm as shown using electron microscopy. Hepatocyte growth factor (HGF), VEGF Receptor 1(Flt-1), collagen type Iα1 and Iα2 mRNA expression levels were observed in the HSC-Li cells by RT-PCR. Immunofluorescence staining showed that the HSC-Li cells were positive for α-smooth muscle actin (α-SMA), platelet-derived growth factor receptor-beta (PDGFR-β), vimentin, and SV40LT protein expression. The HSC-Li cells produced both HGF and transforming growth factor-beta1 (TGF-β1) in a time-dependent manner. Real-time PCR showed that albumin, CYP3A5, CYP2E1, and UGT2B7 mRNA expression generally increased in the co-culture system. The enzymatic activity of CYP1A2 under the co-culture conditions also generally increased as compared to the monoculture of immortalized human hepatocytes.

CONCLUSIONS

We successfully established the immortalized human HSC cell line HSC-Li. It has the specific phenotypic and functional characteristics of primary human HSC, which would be a useful tool to develop anti-fibrotic therapies. Co-culturing with the HSC-Li cells improved the liver-specific functions of hepatocytes, which may be valuable and applicable for bioartificial liver systems.

The Use of Long-term Hepatocyte Cultures for Detecting Induction of Drug Metabolising Enzymes: The Current Status

In this report, metabolically competent in vitro systems have been reviewed, in the context of drug metabolising enzyme induction. Based on the experience of the scientists involved, a thorough survey of the literature on metabolically competent long-term culture models was performed. Following this, a prevalidation proposal for the use of the collagen gel sandwich hepatocyte culture system for drug metabolising enzyme induction was designed, focusing on the induction of the cytochrome P450 enzymes as the principal enzymes of interest. The ultimate goal of this prevalidation proposal is to provide industry and academia with a metabolically competent in vitro alternative for long-term studies. In an initial phase, the prevalidation study will be limited to the investigation of induction. However, proposals for other long-term applications of these systems should be forwarded to the European Centre for the Validation of Alternative Methods for consideration. The prevalidation proposal deals with several issues, including: a) species; b) practical prevalidation methodology; c) enzyme inducers; and d) advantages of working with independent expert laboratories. Since it is preferable to include other alternative tests for drug metabolising enzyme induction, when such tests arise, it is recommended that they meet the same level of development as for the collagen gel sandwich long-term hepatocyte system. Those tests which do so should begin the prevalidation and validation process.

Partial hepatic resistance to IL-6-induced inflammation develops in type 2 diabetic mice, while the anti-inflammatory effect of AMPK is maintained

Interleukin-6 (IL-6) induces hepatic inflammation and insulin resistance, and therapeutic strategies to counteract the IL-6 action in liver are of high interest. In this study, we demonstrate that acute treatment with AMP-activated protein kinase (AMPK) agonists AICAR and metformin efficiently repressed IL-6-induced hepatic proinflammatory gene expression and activation of STAT3 in a mouse model of diet-induced type 2 diabetes, bringing it back to basal nonstimulated level. Surprisingly, the inflammatory response in liver induced by IL-6 administration in vivo was markedly blunted in the mice fed a high-fat diet, compared to lean chow-fed controls, while this difference was not replicated in vitro in primary hepatocytes derived from these two groups of mice. In summary, our work reveals that partial hepatic IL-6 resistance develops in the mouse model of type 2 diabetes, while the anti-inflammatory action of AMPK is maintained. Systemic factors, rather than differences in intracellular IL-6 receptor signaling, are likely mediating the relative impairment in IL-6 effect.

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 tissue engineering and cell sources: issues and challenges

Liver diseases are of major concern as they now account for millions of deaths annually. As a result of the increased incidence of liver disease, many patients die on the transplant waiting list, before a donor organ becomes available. To meet the huge demand for donor liver, alternative approaches using liver tissue engineering principles are being actively pursued. Even though adult hepatocytes, the primary cells of the liver are most preferred for tissue engineering of liver, their limited availability, isolation from diseased organs, lack of in vitro propagation and deterioration of function acts as a major drawback to their use. Various approaches have been taken to prevent the functional deterioration of hepatocytes including the provision of an adequate extracellular matrix and co-culture with non-parenchymal cells of liver. Great progress has also been made to differentiate human stem cells to hepatocytes and to use them for liver tissue engineering applications. This review provides an overview of recent challenges, issues and cell sources with regard to liver tissue engineering.

In vitro models for liver toxicity testing

Over the years, various liver-derived in vitro model systems have been developed to enable investigation of the potential adverse effects of chemicals and drugs. Liver tissue slices, isolated microsomes, perfused liver, immortalized cell lines, and primary hepatocytes have been used extensively. Immortalized cell lines and primary isolated liver cells are currently most widely used in vitro models for liver toxicity testing. Limited throughput, loss of viability, and decreases in liver-specific functionality and gene expression are common shortcomings of these models. Recent developments in the field of in vitro hepatotoxicity include three-dimensional tissue constructs and bioartificial livers, co-cultures of various cell types with hepatocytes, and differentiation of stem cells into hepatic lineage-like cells. In an attempt to provide a more physiological environment for cultured liver cells, some of the novel cell culture systems incorporate fluid flow, micro-circulation, and other forms of organotypic microenvironments. Co-cultures aim to preserve liver-specific morphology and functionality beyond those provided by cultures of pure parenchymal cells. Stem cells, both embryonic- and adult tissue-derived, may provide a limitless supply of hepatocytes from multiple individuals to improve reproducibility and enable testing of the individual-specific toxicity. This review describes various traditional and novel in vitro liver models and provides a perspective on the challenges and opportunities afforded by each individual test system.

Comparison of Basal gene expression in cultured primary rat hepatocytes and freshly isolated rat hepatocytes

Cultured primary hepatocytes are one of the most suitable in vitro models for hepatic toxicological studies. Unfortunately, there is a temporal loss of liver-specific function in culture that limits their utility for some applications. Plating hepatocytes on a substratum has been shown to stabilize the differentiated phenotype for short-term culture. In order to identify the substratum that best supports in vivo basal hepatocyte gene expression profiles in vitro, the gene expression profiles of primary rat hepatocytes plated on collagen I in hepatocyte maintenance medium (HMM) or hepatocyte culture medium (HCM), or on matrigel in HMM medium for 2 h, 16 h, or 72 h were compared to the expression profiles of freshly isolated rat hepatocytes using the Atlas rat stress array. After 16 h in culture, there were differences in gene expression between cultured primary hepatocytes and freshly isolated hepatocytes, but no apparent substratum effects. At 72 h, the expression of 9 genes was altered in hepatocytes plated on either substratum compared to expression in freshly isolated hepatocytes. However, there were an additional 13 genes with increased expression in hepatocytes plated on collagen I that were expressed at low or non-detectable levels in freshly isolated hepatocytes or primary hepatocytes plated on matrigel. In summary, after 72 h, primary hepatocytes plated on matrigel had basal gene expression patterns more similar to patterns in freshly isolated hepatocytes than did hepatocytes cultured on collagen. In addition, culture on matrigel suppressed the expression of atypical genes in culture. These preliminary studies suggest that culture on matrigel may be preferable for longer-term in vitro toxicological studies.

Three-dimensional co-culture of hepatocytes and stellate cells

Hepatocytes self-assemble in culture to form compacted spherical aggregates, or spheroids, that mimic the structure of the liver by forming tight junctions and bile canalicular channels. Hepatocyte spheroids thus resemble the liver to a great extent. However, liver tissue contains other cell types and has bile ducts and sinusoids formed by endothelial cells. Reproducing 3-D co-culture in vitro could provide a means to develop a more complex tissue-like structure. Stellate cells participate in revascularization after liver injury by excreting between hepatocytes a laminin trail that endothelial cells follow to form sinusoids. In this study we investigated co-culture of rat hepatocytes and a rat hepatic stellate cell line, HSC-T6. HSC-T6, which does not grow in serum-free spheroid medium, was able to grow under co-culture conditions. Using a three-dimensional cell tracking technique, the interactions of HSC-T6 and hepatocyte spheroids were visualized. The two cell types formed heterospheroids in culture, and HSC-T6 cell invasion into hepatocyte spheroids and subsequent retraction was observed. RT-PCR revealed that albumin and cytochrome P450 2B1/2 expression were better maintained in co-culture conditions. These three-dimensional heterospheroids provide an attractive system for in vitro studies of hepatocyte-stellate cell interactions.

Evaluation of a hepatocyte-entrapment hollow fiber bioreactor: a potential bioartificial liver

We have developed a hepatocyte entrapment hollow fiber bioreactor for potential use as a bioartificial liver. Hepatocytes were entrapped in collagen gel inside the lumen of the hollow fibers. Medium was perfused through the intraluminal region after contraction of the hepatocyte-entrapment gel. Another medium stream, comparable to the patient's blood during clinical application, passed through the extracapillary space. Viability of hepatocytes remained high after 5 days as judged by the rate of oxygen uptake and viability staining. Urea and albumin synthetic activities were also sustained. Transmission electron microscopic examination demonstrated normal ultrastructural integrity of hepatocytes in such a bioreactor. With its sort-term, extracorporeal support of acute liver failure, the current bioreactor warrants further investigation.

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

Hepatocytes are the preparation of choice for Toxicological research in vitro. However, despite the fact that hepatocytes proliferate in vivo during liver regeneration, they are resistant to proliferation in vitro, do not tolerate sub-culture and tend to enter a de-differentiation program that results in a loss of hepatic function. These limitations have resulted in the search for expandable rodent and human cells capable of being directed to differentiate into functional hepatocytes. Research with stem cells suggests that it may be possible to provide the research community with hepatocytes in vitro although to date, significant challenges remain, notably generating a sufficiently pure population of hepatocytes with a quantitative functionality comparable with hepatocytes. This paper reviews work with the AR42J-B-13 (B-13) cell line. The B-13 cell was cloned from the rodent AR42J pancreatic cell line, express genes associated with pancreatic acinar cells and readily proliferates in simple culture media. When exposed to glucocorticoid, 75-85% of the cells trans-differentiate into hepatocyte-like (B-13/H) cells functioning at a level quantitatively similar to freshly isolated rat hepatocytes (with the remaining cells retaining the B-13 phenotype). Trans-differentiation of pancreatic acinar cells also appears to occur in vivo in rats treated with glucocorticoid; in mice with elevated circulating glucocorticoid and in humans treated for long periods with glucocorticoid. The B-13 response to glucocorticoid therefore appears to be related to a real pathophysiological response of a pancreatic cell to glucocorticoid. An understanding of how this process occurs and if it can be generated or engineered in human cells would result in a cell line with the ability to generate an unlimited supply of functional human hepatocytes in a cost effective manner.

Liver-specific functional studies in a microfluidic array of primary mammalian hepatocytes

Nearly half a billion dollars in resources are lost each time a drug candidate is withdrawn from the market by the Food and Drug Administration (FDA) for reasons of liver toxicity. The number of late-phase drug developmental failures due to liver toxicity could potentially be reduced through the use of hepatocyte-based systems capable of modeling the response of in vivo liver tissue to toxic insults. With this article, we report progress toward the goal of realizing an array of primary hepatocytes for use in high-throughput liver toxicity studies. Described herein is the development of a 64 (8 x 8) element array of microfluidic wells capable of supporting micropatterned primary rat hepatocytes in coculture with 3T3-J2 fibroblasts. Each of the wells within the array was continuously perfused with medium and oxygen in a nonaddressable format. The key features of the system design and fabrication are described, including the use of two microfluidic perfusion networks to provide the coculture with an independent and continuous supply of cell culture medium and oxygen. Also described are the fabrication techniques used to selectively pattern hepatocytes and 3T3-J2 fibroblasts within the wells of the array. The functional studies used to demonstrate the synthetic and metabolic capacity of the array are outlined in this article. These studies demonstrate that the hepatocytes contained within the array are capable of continuous, steady-state albumin synthesis (78.4 microg/day, sigma = 3.98 microg/day, N = 8) and urea production (109.8 microg/day, sigma = 11.9 microg/day, N = 8). In the final section of the article, these results are discussed as they relate to the final goal of this research effort, the development of an array of primary hepatocytes for use in physiologically relevant toxicology studies.

Hepatocellular expression of glutamine synthetase: an indicator of morphogen actions as master regulators of zonation in adult liver

Glutamine synthetase (GS) has long been known to be expressed exclusively in pericentral hepatocytes most proximal to the central veins of liver lobuli. This enzyme as well as its peculiar distribution complementary to the periportal compartment for ureogenesis plays an important role in nitrogen metabolism, particularly in homeostasis of blood levels of ammonium ions and glutamine. Despite this fact and intensive studies in vivo and in vitro, many aspects of the regulation of its activity on the protein and on the genetic level remained enigmatic. Recent experimental advances using transgenic mice and new analytic tools have revealed the fundamental role of morphogens such as wingless-type MMTV integration site family member signals (Wnt), beta-catenin, and adenomatous polyposis coli in the regulation of this particular enzyme. In addition, novel information concerning the structure of transcription factor binding sites within regulatory regions of the GS gene and their interactions with signalling pathways could be collected. In this review we focus on all aspects of the regulation of GS in the liver and demonstrate how the new findings have changed our view of the determinants of liver zonation. What appeared as a simple response of hepatocytes to blood-derived factors and local cellular interactions must now be perceived as a fundamental mechanism of adult tissue patterning by morphogens that were considered mainly as regulators of developmental processes. Though GS may be the most obvious indicator of morphogen action among many other targets, elucidation of the complex regulation of the expression of the GS gene could pave the road for a better understanding of the mechanisms involved in patterning of liver parenchyma. Based on current knowledge we propose a new concept of how morphogens, hormones and other factors may act in concert, in order to restrict gene expression to small subpopulations of one differentiated cell type, the hepatocyte, in different anatomical locations. Although many details of this regulatory network are still missing, and an era of exciting new discoveries is still about to come, it can already be envisioned that similar mechanisms may well be active in other organs contributing to the fine-tuning of organ-specific functions.

Hepatocyte hollow-fibre bioreactors: design, set-up, validation and applications

Hepatocytes carry out many vital biological functions, such as synthetic and catabolic reactions, detoxification and excretion. Due to their ability to restore a tissue-like environment, hollow-fibre bioreactors (HFBs) show great potential among the different systems used to culture hepatocytes. Several designs of HFBs have been proposed in which hepatocytes or hepatocyte-derived cell lines can be cultured in suspensions or on a solid support. Currently the major use of hepatocyte HFBs is as bioartificial livers to sustain patients suffering from acute liver failure, but they can also be used to synthesize cell products and as cellular models for drug metabolism and transport studies. Here, we present an overview of the set-up of hepatocyte HFBs and aim to provide potential users with the basic knowledge necessary to develop their own system. First, general information on HFBs is given, including basic principles, transport phenomena, designs and cell culture conditions. The importance of the tests necessary to assess the performance of the HFBs, i.e. the viability and functionality of hepatocytes, is underlined. Special attention is paid to drug metabolism studies and to adequate analytical methods. Finally, the potential uses of hepatocyte HFBs are described.

The effect of three-dimensional co-culture of hepatocytes and hepatic stellate cells on key hepatocyte functions in vitro

In this study, we demonstrate the ability of a three-dimensional co-culture model to preserve some key aspects of differentiated hepatocyte function in vitro. Freshly isolated rat hepatocytes in co-culture with activated stellate cells rapidly aggregate to form well-defined viable spheroids. After 5 days in culture, the spheroids have a complex extracellular matrix support and hepatic ultrastructure including bile canaliculi, tight junctions, desmosomes and lipid storage. Co-culture spheroids have superior cytochrome P450 (CYP450) 3A and 2B function, and increased inducibility of 2B function, relative to a range of hepatocyte monoculture techniques (high-performance liquid chromatography of testosterone metabolites). Increased function in co-culture is supported by greater expression of CYP450 3A23, 1A2, and 2E1 mRNA relative to monoculture (reverse transcriptase quantitative polymerase chain reaction). Also, high hepatocyte growth factor mRNA expression in co-culture suggests a post-traumatic, or possibly regenerative, environment. A preliminary study of human hepatocytes co-cultured with rat stellate cells demonstrated prolonged function of CYP450 3A4, 2C19 and 2C9. This study shows that stellate cells facilitate spheroid formation, influence spheroid architecture, and are an effective method of preserving some aspects of hepatocyte function in the early stage of culture.

Liver endothelial cells promote LDL-R expression and the uptake of HCV-like particles in primary rat and human hepatocytes

Low-density lipoprotein (LDL) is an important carrier of plasma cholesterol and triglycerides whose concentration is regulated by the liver parenchymal cells. Abnormal LDL regulation is thought to cause atherosclerosis, while viral binding to LDL has been suggested to facilitate hepatitis C infection. Primary hepatocytes quickly lose the ability to clear LDL during in vitro culture. Here we show that the coculture of hepatocytes with liver sinusoidal endothelial cells (LSEC) significantly increases the ability of hepatocytes to uptake LDL in vitro. LDL uptake does not increase when hepatocytes are cocultured with other cell types such as fibroblasts or umbilical vein endothelial cells. We find that LSECs induce the hepatic expression of the LDL receptor and the epidermal growth factor receptor. In addition, while hepatocytes in single culture did not take up hepatitis C virus (HCV)-like particles, the hepatocytes cocultured with LSECs showed a high level of HCV-like particle uptake. We suggest that coculture with LSECs induces the emergence of a sinusoidal surface in primary hepatocytes conducive to the uptake of HCV-like particles. In conclusion, our findings describe a novel model of polarized hepatocytes in vitro that can be used for the study of LDL metabolism and hepatitis C infection.

INVESTIGATION OF A HEPATOTOXICITY SCREENING SYSTEM IN PRIMARY CELL CULTURES-"WHAT BIOMARKERS WOULD NEED TO BE ADDRESSED TO ESTIMATE TOXICITY IN CONVENTIONAL AND NEW APPROACHES?"-

High throughput toxicological estimation is required for safety evaluation in the early stage of drug discovery. In this context, establishment of an in vitro screening system reflecting in vivo toxicity is demanded for earlier safety assessment. We investigated LDH release and mitochondrial respiration (WST-1 reduction assay; WST-1) to detect cytotoxicity, morphological evaluation, and proteomics for estimating the reliable and sensitive biomarkers by using rat primary hepatocytes exposed to the compounds (acetaminophen, amiodarone, tetracycline and carbon tetrachloride) that are known to induce hepatotoxicity. In LDH release, no significant difference was detected between the control and compound exposed cells after exposure for 3 or 6 hr, but a dose-dependent increase was observed after exposure for 24 hr. Regarding the WST-1 assay, a dose-dependent reduction was detected after exposure for 6 and 24 hr to all of the compounds evaluated. In the proteomics analysis, 31 candidate proteins were identified from among the 103 demonstrating altered expression spots after exposure to acetaminophen. It was concluded that the cytotoxicity was detected earlier by measuring WST-1 than by measuring LDH release because the reduction of mitochondrial respiration is an expressions of earlier toxicity for cellular function, while the measured increase in the LDH release occurs after the failure of the cell membrane. Mitochondrial respiration ability was a useful parameter for cytotoxicity in in vitro hepato-toxicity screening, as cytotoxicity can be detected during the early stage of exposure. In addition to the conventional biomarkers, several protein biomarkers which relate to oxidative stress and metabolism-regulation were detected. Further comprehensive analysis of defined proteins would be necessary to estimate the more sensitive toxicology biomarker.

Impact of serum on clearance predictions obtained from suspensions and primary cultures of rat hepatocytes

The objective of the present study was to compare two configurations of the hepatocyte model namely suspensions (SH) and conventional primary cultures (CPC) for their ability to predict the hepatic clearance in vivo in the rat and, to investigate the impact of serum on the prediction accuracy. The metabolic competences of several cytochrome P450 isoenzymes were investigated both in CPC and SH in the presence or absence of serum. Under the same conditions, the in vitro intrinsic clearance of six test compounds metabolised by a variety of phase I and phase II enzymes (antipyrine, RO-X, mibefradil, midazolam, naloxone and oxazepam) were derived from Vmax/Km scaled up to the corresponding in vivo hepatic metabolic clearance. CYP activities were shown to be stable in both CPC and SH for up to 6 h of incubation, except for the CYP 3A1 activity that decreased in CPC even in the presence of serum. Moreover, the clearances predicted from SH in the presence of serum were closer to the in vivo values than those obtained from CPC. SH represent a convenient model to assess the hepatic metabolism of xenobiotics, the presence of serum in the incubation medium significantly improved in several instances the quality of the predictions.

Induction and regulation of acute phase proteins in transdifferentiated hepatocytes

Acute phase proteins (APPs) are predominantly synthesized in the liver and play an important role in restoring homeostasis. In the present study, we set out to answer two questions using transdifferentiated hepatocytes induced from pancreatic cells as a model for studying the acute phase response. Firstly, do transdifferentiated hepatocytes express acute phase proteins following culture with glucocorticoid and cytokines? Secondly, what is the molecular basis of the induction of acute phase proteins in transdifferentiated hepatocytes? Hepatic transdifferentiation was induced in 11.5-day mouse embryonic pancreas or the pancreatic cell line AR42J-B13 (B13) by culture with dexamethasone. We found that acute phase proteins [alpha2-macroglobulin (MG), haptoglobin (Hp)] were induced in both systems following culture with dexamethasone. The combined treatment of dexamethasone and oncostatin M (OSM) enhanced the expression of the acute phase proteins in B13 cells and the mechanism of the up-regulation by the cytokine is probably mediated by phosphorylation of STAT3 and STAT1. In addition, ectopic expression of either C/EBPbeta or C/EBPalpha in B13 cells induced haptoglobin expression and culture with oncostatin M was sufficient to enhance the expression of haptoglobin in C/EBPbeta transfected cells from 18% to 43%. The results of the present study indicate transdifferentiated hepatocytes have the potential to be a useful model to study liver function in vitro.

Establishment of immortalized human hepatic stellate scavenger cells to develop bioartificial livers

BACKGROUND

Maintenance of liver-specific functions has been shown to be stabilized by co-cultivation of hepatocytes with hepatic stellate cells (HSC). Because the limited lifespan of human HSC is a major hurdle to their use, the authors report here the amplification of human HSC populations in vitro by retroviral transfer of human telomerase reverse transcriptase (hTERT).

METHODS

Human HSC strain LI 90 cells were transduced with a retroviral vector SSR#197 expressing hTERT and green fluorescent protein (GFP) cDNA flanked by a pair of loxP. TWNT-1, one of SSR#197-immortalized HSC, was characterized. Differentiated liver functions were evaluated in an immortalized human hepatocyte NKNT-3-TWNT-1 co-culture system.

RESULTS

TWNT-1 cells showed differential functions of HSC, including uptake of acetylated low-density lipoproteins and synthesis of collagen type I and hepatocyte growth factor. Efficient excision of the retrovirally transferred hTERT and GFP cDNAs was achieved by TAT-mediated expression of the Cre recombinase and subsequent GFP-negative cell sorting. When co-cultured with TWNT-1 cells, NKNT-3 increased protein expression of the detoxifying cytochrome P450-associated protein isoenzymes 3A4 and 2C9 and urea synthesis.

CONCLUSIONS

TWNT-1 cells could be valuable in the study of integrated liver functions and contribute to the optimization of liver cell therapies and bioartificial livers.

Long-term culture of functional liver tissue: three-dimensional coculture of primary hepatocytes and stellate cells

One of the greatest challenges in the attempt to create functional liver tissue in vitro is the maintenance of hepatocyte-specific functions. The pharmaceutical industry has long awaited the development of engineered liver tissue, which could represent a long-term, inducible, high-fidelity model for high-throughput screening of new drug compounds. It is also anticipated that such engineered models could one day be used in liver transplants, where replacement is limited by chronic donor shortages. As isolated hepatocytes dedifferentiate rapidly in culture the use of hepatocytes in long-term studies has proved to be a difficult challenge. Here we report a system of rat hepatocytes cocultured with primary rat hepatic stellate cells on a biodegradable poly(DL-lactic acid) substratum. These coculture conditions were found to encourage the rapid self-organization of three-dimensional spheroids. The spheroids formed exhibit hepatocyte-specific functionality (CYP-450 activity and albumin secretion) after almost 2 months in static culture.

Advantages of in vitro cytotoxicity testing by using primary rat hepatocytes in comparison with established cell lines

We investigated and compared the cytotoxicity of 16 reference compounds in four in vitro systems: primary cultured rat hepatocytes, hepatoma HepG2 cell line, non-hepatic HeLa and Balb/c 3T3 cell lines. After 24 hr of exposure to the test compounds, the water-soluble tetrazolium salts WST-1 assay was used as an endpoint to evaluate cytotoxicity. Acetaminophen, diclofenac sodium cyclophosphamide and disulfiram displayed from 2 to more than 10 times higher IC50 values in three cell lines than in rat primary cultured hepatocytes. The cytotoxic effects of aspirin, amiodarone, clorfibiric acid, chlorpromazine, erythomycin, lithocholic acid, cisplatin and quinidine in rat hepatocytes were similar or 2 times stronger than those observed in cell lines. Ketoconazole resulted in the lowest IC50 value in the HeLa cell line. The data suggested that the compounds which are known to be metabolism-mediated liver toxicants have a differential hepatotoxicity in vitro and that primary cultured rat hepatocytes could represent a valuable tool for both screening and study of the effects of bio-transformation on the cytotoxicity of new chemical entities and xenobiotics in vitro.

Effect of oxygen concentration on the expression of glutathione S-transferase activity in periportal and perivenous rat hepatocyte cultures

Cultures of perivenous (PV) and periportal (PP) hepatocytes could provide suitable in vitro models for studying the zone-specific hepatotoxic potential of xenobiotics. However, it is not known whether cultured PP and PV hepatocytes keep their phenotypes when the microcirculation of the liver changes. This question has been studied by culturing rat hepatocytes at 13 and 4% (v/v) O(2), respectively, mimicking the acinar oxygen gradient. PP and PV adult rat hepatocytes were isolated by digitonin-collagenase in situ perfusion and cultured on plastic Falcon and gas-permeable Petriperm dishes in Williams' E medium and kept at 13 and 4% (v/v) O(2), respectively. Cultures at 20% (v/v) O(2) on plastic dishes served as a control. Two types of cultures were studied, namely conventional cultures either unsupplemented or supplemented with 30 mM pyruvate. The activities of glutamine synthetase (GS) and glutathione S-transferase (GST) were measured in freshly isolated PP and PV hepatocytes and all cultures. The heterogeneous expression of GS (PV>PP), observed in freshly isolated hepatocytes, was kept for at least 4 days in culture. Total, Mu and Alpha class GST activities were predominantly expressed in PV freshly isolated cells. However, no beneficial effect could be observed in culture by exposing the cells to their specific in vivo oxygen concentration. The best maintenance of GST PV predominance in culture was observed in Petriperm dishes at 20% (v/v) O(2), as well in pyruvate-supplemented as unsupplemented cultures. PV GST predominance was thus kept in particular when the highest oxygen concentration was used and made available to the cells through the gas-permeable membranes. The results on GS PV predominance support these findings.

Ductular morphogenesis and functional polarization of normal human biliary epithelial cells in three-dimensional culture

BACKGROUND/AIMS

The understanding of the physiology and function of human biliary epithelial cells (hBEC) has been improved by studies in monolayer culture systems. The aim was to develop a polarized model to elucidate the mechanisms of ductular morphogenesis and functional differentiation of hBEC.

METHODS

The morphological, phenotypic and functional properties of hBEC cultured as three-dimensional aggregates in collagen gel were assessed in medium supplemented with (or without) human hepatocyte growth factor (hHGF) and foetal bovine serum.

RESULTS

In the absence of added mitogens and serum, cells maintained as morphologically polarized aggregates, organized around a central lumen, were positive for phenotypic markers of biliary epithelium and negative for markers of other cell types. Functional markers, gamma-glutamyl-transferase, anion exchanger-2, responses to gamma interferon and forskolin induced secretion, were preserved. hHGF increased both the size and number of aggregates and induced hBEC to invade the gel and lumena forming anastomosing networks of cells.

CONCLUSIONS

Collagen gel culture in the absence of added growth factors and serum provides a model for analysis of the polarized functions of hBEC. The formation of poorly organized cords of cells in response to hHGF suggests that collagen gel culture may provide a model for the investigation of atypical ductular morphogenesis of the human biliary tract.

Predictive value of in vitro model systems in toxicology

The application of in vitro model systems to evaluate the toxicity of xenobiotics has significantly enhanced our understanding of drug- and chemical-induced target toxicity. From a scientific perspective, there are several reasons for the popularity of in vitro model systems. From the public perspective, in vitro model systems enjoy increasing popularity because their application may allow a reduction in the number of live animals employed in toxicity testing. In this review, we present an overview of the use of in vitro model systems to investigate target organ toxicity of drugs and chemicals, and provide selective examples of these model systems to better understand cutaneous and ocular toxicity and the role of drug metabolism in the hepatotoxicity of selected agents. We conclude by examining the value and use of in vitro model systems in industrial development of new pharmaceutical agents.

Selective induction of cytochrome P450 3A1 by dexamethasone in cultured rat hepatocytes: analysis with a novel reverse transcriptase-polymerase chain reaction assay section sign

The study of drug metabolism in cultured rat hepatocytes is hampered by the rapid loss of the expression of cytochrome P450 enzymes. Nevertheless, the activity of cytochrome P450 3A (CYP3A), one of the most important isoenzymes for drug metabolism, can be elevated by chemical inducers. In the present study, we investigated in cultured rat hepatocytes the induction of all four currently identified CYP3A isoforms by dexamethasone, and compared the results obtained in vitro with the induction profile of dexamethasone in vivo. To this end, CYP3A mRNA levels were quantified with a novel, radioactive reverse transcriptase-polymerase chain reaction (RT-PCR) assay, and CYP3A enzymatic activity was measured by a testosterone hydroxylation assay. In the RT-PCR assay, CYP3A isoforms were co-amplified with glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in the presence of radioactively labeled nucleotides. This resulted in an extremely sensitive and accurate determination of CYP3A expression levels, relative to those of GAPDH. Using this RT-PCR assay, it was found that the expression of all CYP3A isoforms in rat hepatocytes, cultured on a collagen matrix, was decreased by 80-90% within one day of cultivation. After addition of dexamethasone, at one day after isolation, CYP3A1 mRNA levels were elevated to levels comparable to those in freshly isolated hepatocytes within two days. In contrast, CYP3A2, CYP3A9, and CYP3A18 mRNA levels were not affected by dexamethasone treatment, and were hardly detectable after three days of cultivation. CYP3A enzymatic activity was also induced in cultured hepatocytes (approximately 6-fold) after addition of dexamethasone. In vivo, CYP3A1 mRNA levels increased 45-fold after dexamethasone administration. However, in contrast to the situation in cultured hepatocytes, CYP3A2 and CYP3A18 were also induced, albeit to a lesser extent (4- and 7-fold elevated mRNA levels, respectively). We conclude that the selective induction of CYP3A1 in dexamethasone-treated rat hepatocytes allows the study of biotransformation reactions by CYP3A1, without interference by any of the other CYP3A isoenzymes.

Effect of cell-cell interactions in preservation of cellular phenotype: cocultivation of hepatocytes and nonparenchymal cells

Heterotypic cell interaction between parenchymal cells and nonparenchymal neighbors has been reported to modulate cell growth, migration, and/or differentiation. In both the developing and adult liver, cell-cell interactions are imperative for coordinated organ function. In vitro, cocultivation of hepatocytes and nonparenchymal cells has been used to preserve and modulate the hepatocyte phenotype. We summarize previous studies in this area as well as recent advances in microfabrication that have allowed for more precise control over cell-cell interactions through 'cellular patterning' or 'micropatterning'. Although the precise mechanisms by which nonparenchymal cells modulate the hepatocyte phenotype remain unelucidated, some new insights on the modes of cell signaling, the extent of cell-cell interaction, and the ratio of cell populations are noted. Proposed clinical applications of hepatocyte cocultures, typically extracorporeal bioartificial liver support systems, are reviewed in the context of these new findings. Continued advances in microfabrication and cell culture will allow further study of the role of cell communication in physiological and pathophysiological processes as well as in the development of functional tissue constructs for medical applications.

Characterization and evaluation of detoxification functions of a nontumorigenic immortalized porcine hepatocyte cell line (HepLiu)

Primary porcine hepatocytes (PPH) are currently used in research and therapeutic applications as the biological component of extracorporeal liver assist devices to overcome the shortage of human hepatocytes. However, their finite life span and typically rapid loss of functions limit their utility. An immortalized, nontumorigenic, highly differentiated porcine hepatocyte cell line was developed in our laboratory to resolve these disadvantages. PPH were transfected with simian virus 40 (SV40) T antigen under the control of the SV40 early promoter. From the established 69 clones, 23 clones displaying hepatocyte-like morphology were screened for diazepam metabolism. One clone, HepLiu D63, has been maintained in culture for > 2 years, through more than 60 passages and 240 divisions. Albumin protein, present in early passages, was lost at later passages, but albumin transcript still was detectable in later passages. Carbamoyl phosphate synthetase, a gateway enzyme of the urea cycle, was consistently detectable in HepLiu cells. Cytokeratin 18, a characteristic marker of primary hepatocytes, was detected by both immunofluorescent staining and Western blot in HepLiu cells. Furthermore, maintenance of P450 functions in HepLiu cells was evidenced by diazepam and 7-ethoxycoumarin metabolites measured by HPLC. Phase II conjugative function was measured as acetaminophen glucuronidation. P450 dealkylase was demonstrated microscopically by the conversion of a nonfluorescent substrate to a fluorescent product. Both Northern blot analysis and immunofluorescent staining showed SV40 T antigen expression in the nuclei of HepLiu cells. No tumor formation occurred when HepLiu cells were injected into severe combined immunodeficient (SCID) mice nor was the TAI (a tumor marker) mRNA expressed, even in later passages. This immortalized, nontumorigenic, highly functional cell line may provide a valuable tool for drug/toxicological studies, liver biologic regulation studies, and artificial liver support systems.

Analysis of cytochrome P450 and phase II conjugating enzyme expression in adult male rat hepatocytes

The induction of cytochrome P450 (CYP450) and Phase II conjugating enzymes by prototypical hepatic enzyme inducers was studied in adult male rat hepatocytes. Hepatocytes were suspended and cultured in diluted Matrigel in a basal serum-free Dulbecco's modified Eagle medium and exposed to the prototypical liver enzyme inducers, 3-methylcholanthrene, phenobarbital, hydrocortisone, and clofibrate for 48 h. Total RNA and microsomes were isolated and prepared, respectively, at 72 h. The expression of CYP1A1, CYP1A2, CYP2B1, CYP2C11, CYP2E1, CYP3A1, CYP3A2, CYP4A1, fatty acyl-CoA oxidase, uridine diphosphate-glucuronosyltransferase, glutathione-S-transferase, and sulfotransferase was determined at the mRNA level with reverse transcriptase polymerase chain reaction (RT-PCR). The expression of CYP1A1, CYP2B1, CYP2C11, CYP2E1, and CYP4A1 was also measured at the apoprotein level by Western immunoblotting. Using these culture and expression analysis techniques, we have found that the expression of these metabolic enzymes can be maintained in culture for up to 7 d at the mRNA and apoprotein levels. In addition, hepatocytes were found to respond to chemical enzyme inducers with marked increases in enzyme expression at either the mRNA or protein level and in a concentration-related fashion. Cells were responsive to enzyme induction as early as 24 h after initial plating. The results obtained from this investigation indicate that the presence of diluted Matrigel (at a concentration of 0.35 mg/ml), the use of low concentrations of insulin (1 microM), hydrocortisone (0.1 microM), and serum-free culture medium can maintain the differentiated phenotype and responsiveness of cultured hepatocytes to chemical-induced metabolic enzyme expression. Under the conditions used in this study, enzyme induction in adult male rat hepatocytes shows close agreement with enzyme induction observed in the livers of rats exposed to these or similar prototypical enzyme inducers. Rat hepatocytes cultured in the presence of diluted Matrigel coupled with enzyme mRNA expression analysis with RT-PCR are proven to be a valuable and important in vitro toxicological approach to assess the chemical-induced changes in expression of liver CYP450 and Phase II conjugating enzymes.

Bgugaine, a pyrrolidine alkaloid from Arisarum vulgare, is a strong hepatotoxin in rat and human liver cell cultures

Toxicity of bgugaine, a pyrrolidine alkaloid extracted from the tubers of Arisarum vulgare, was studied in three different liver cell culture models: (1) the rat hepatocyte primary culture; (2) a liver epithelial cell line; and (3) the human hepatoblastoma cell line HepG2. Cytotoxicity was evaluated by LDH release, MTT reduction and MDA production. DNA fragmentation was analysed by flow cytometry or DNA gel-electrophoresis. In hepatocyte and epithelial cell cultures, drug toxicity appeared at 30 microM and was evaluated by an increase in LDH release, a decrease in MTT reduction and a higher level of MDA production. Bgugaine concentrations lower than 30 microM did not induce changes in these parameters. In HepG2 cells, bgugaine treatment also induced LDH release at concentrations of 40 and 50 microM. DNA fragmentation, analysed in the HepG2 cell line by flow cytometry, was observed in cultures exposed to 50 microM bgugaine. However, using DNA gel-electrophoresis, we demonstrated that lower bgugaine concentrations (10, 20 and 30 microM) also induced DNA damage. Our results show that: (1) bgugaine induces an important hepatotoxicity; (2) bgugaine toxicity is not mediated by a metabolic derivative; and (3) bgugaine induces a significant DNA damage. Therefore, our data suggest that the alkaloid bgugaine contained in Arisarum vulgarae may be involved in the toxicologic symptoms observed after consumption of this plant tubers by humans and animals.

Endogenous nitric oxide is responsible for the early loss of P450 in cultured rat hepatocytes

Loss of P450 during the early hours of monolayer formation is known to be the more serious limitation of primary cultured hepatocytes as an adequate model for the study of drug metabolism, toxicity and P450 induction. This study reports that endogenous nitric oxide (NO) formation is activated shortly after isolation by the classical collagenase-based liver perfusion methods. Both rapid P450 loss and aerobic mitochondrial energy metabolism impairment -- with subsequent changes on glucose metabolism -- are directly related to the high local generation of the radical at this stage. These effects can be reverted by the sole addition of NO biosynthesis inhibitors during liver perfusion and early culture hours, which allows catalytically active P450 to be preserved at levels close to those of the intact liver.

Rodent hepatocarcinogenic peroxisome proliferators induce proliferation of rat hepatocytes in primary mixed cultures with rat liver epithelial cells

The effect of two members of the hypolipidemic medicine class of hepatocarcinogenic peroxisome proliferators on proliferation of hepatocytes in primary mixed cultures with liver epithelial cells was studied. Rat hepatocytes present in primary mixed cultures with rat liver epithelial cells were maintained for 3 months retaining their differentiated characteristics and proliferative potential. Hepatocyte clusters in mixed cultures stained positive for albumin, indicating that they retained some metabolic functions. Furthermore, in mixed cultures exposed to 0.2 mM clofibric acid or ciprofibrate for 3 months, hepatocytes were engaged in proliferation as shown by the expression of proliferating cell nuclear antigen (PCNA) and the presence of mitotic figures. This in vitro system could be useful to obtain more information about responses of liver cells during prolonged exposure to peroxisome proliferators.

Influence of 48 hours of cold storage in University of Wisconsin organ preservation solution on metabolic capacity of rat hepatocytes

BACKGROUND/AIMS

Suspensions of isolated hepatocytes are a valuable tool to study liver functions. For optimal use of the isolated hepatocytes, methods are needed to preserve the hepatocytes while maintaining their viability, metabolic and transport functions. Until now, little has been known about the maintenance of the drug metabolism capacity and energy state, measured by the so-called energy charge (ATP+1/2ADP)/(ATP+ADP+AMP), in hepatocytes after storage in University of Wisconsin cold storage solution (UW). Consequently, we investigated whether UW, originally designed to preserve organs for transplantation, was suitable for preservation of isolated rat hepatocytes with respect to the maintenance of drug metabolism and levels of energy-rich substrates.

METHODS

Viability of the isolated rat hepatocytes was determined by trypan blue exclusion, ATP content and energy charge after 24 and 48 h of storage in UW at 0 degrees C. Phase I and II metabolic functions of the cells were studied by measuring the cytochrome P450 content and the metabolic rate of lidocaine and 7-ethoxycoumarin.

RESULTS

During 48 h of storage of hepatocytes in UW both phase I and phase II metabolism are preserved at control levels. After storage, the viability of the hepatocytes was not changed significantly, and the cells maintained proper cellular ATP content and overall energy charge.

CONCLUSIONS

These results imply that hepatocytes from a single isolation can be stored in UW solution and used for metabolism experiments for 3 consecutive days, allowing a reduction in the use of experimental animals.

Effect of pyridine on the expression of cytochrome P450 isozymes in primary rat hepatocyte culture

In vivo administration of pyridine has been shown to increase the activity and content of several forms of cytochrome P450 by transcriptional and posttranscriptional mechanisms. The effect of pyridine on CYP1A and CYP2E1 isozymes was studied in a rat hepatocyte culture model. Hepatocytes were isolated from non-induced rats and seeded onto matrigel-coated dishes and incubated in William's medium E containing 10% fetal calf serum, hormones, and essential metals. Cultures were treated with 0, 10 or 25 mM pyridine for 1-3 days and microsomes were isolated to determine catalytic activity and for immunoblot analysis, and total RNA was isolated for mRNA determinations. CYP2E1 content, CYP2E 1 mRNA, and CYP2E1 catalyzed oxidation of p-nitrophenol declined during culture to values of 3, 30 and 19% that of initial, non-cultured controls by day 3 of culture. Pyridine prevented this decline of CYP2E1 protein and activity such that 60-80% original activity remained after 3 days of culture in the presence of 25 mM pyridine. However, pyridine did not prevent the fall in CYP2E1 mRNA levels, nor did pyridine increase the content or activity of CYP2E1 above initial values of microsomes from freshly isolated hepatocytes. Pyridine increased the content of CYP1A2 and the oxidation of ethoxyresorufin 2-4 fold compared to cultures incubated without pyridine over the 3 day culture period. CYP1A1 levels, which rapidly declined, were induced and maintained in the presence of pyridine. Pyridine increased CYP1A content and activity 2-3 fold over initial values of freshly isolated hepatocytes. These increases were associated with corresponding increases in CYP1A mRNA levels. CYP1A2, but not CYP1A1, mRNA levels increased in the cultures incubated in the absence of pyridine. These results indicate that pyridine has different effects on CYP1A and CYP2E1 in this hepatocyte culture model. Pyridine appears to modulate CYP2E1 levels by posttranscriptional mechanisms as CYP2E1 activity and content were maintained in the presence of pyridine under conditions in which CYP2E1 mRNA levels declined. These mechanisms may involve increased translational efficiency of existing CYP2E1 mRNA or stabilization of CYP2E1 protein against degradation. Pyridine increased CYP1A1 and CYP1A2 content, activity and mRNA levels, either inducing CYP1A transcription or stabilizing CYP1A mRNA. Hepatocyte cultures may be a useful model to study the interaction of pyridine with P450 isozymes and their associated drug-mediated toxicity.

Extended primary culture of human hepatocytes in a collagen gel sandwich system

To develop a strategy for extended primary culture of human hepatocytes, we placed human hepatocytes between two layers of collagen gel, called a "collagen gel sandwich." Maintenance of hepatocellular functions in this system was compared with that of identical hepatocyte preparations cultured on dry-collagen coated dishes or cocultured with rat liver epithelial cells. Human hepatocytes in a collagen gel sandwich (five separate cultures) survived for more than 4 wk, with the longest period of culture being 78 d. They maintained polygonal morphology with bile canaliculuslike structures and high levels of albumin secretion throughout the period of culture. In contrast, hepatocytes on dry-collagen became feature-less, and albumin secretion could not be detected after 14 d of culture. This loss of albumin secretion was partially recovered by overlaying one layer of collagen gel. Ethoxyresorufin O-deethylase activity, associated with cytochrome P450 1A2, was detected basally up to 29 d in collagen gel sandwich culture. These activities were induced four- to eightfold after induction with dibenz(a,h)anthracene. Cocultures also maintained basal activity up to 29 d. However, their inducibility was lower than that of hepatocytes in collagen gel sandwich. No ethoxyresorufin O-deethylase activity was detected in hepatocytes cultured on dry-collagen at 7 d. Thus, the collagen gel sandwich system preserves differentiated morphology and functions of human hepatocytes in primary culture for a prolonged period of time. This system is a promising model for studying human hepatocellular function, including protein synthesis and drug metabolism in vitro.

Lipid-mediated transfection of normal adult human hepatocytes in primary culture

The aim of this work was to develop a procedure for the lipid-mediated transfection of DNA into normal adult human hepatocytes in culture. Cells were plated in a serum-free culture medium at various cell densities, on plastic or collagen-coated dishes, both in the absence and in the presence of epidermal growth factor (EGF). The cells were incubated for various periods of time with mixtures of DNA-lipofectin or DNA-3 beta[N-(N',N'-dimethylaminoethane)-carbamoyl] cholesterol (DC-chol) liposomes, and the efficiency of transfection was assessed by measuring the activity of reporter genes, beta-galactosidase or chloramphenicol acetyl-transferase (CAT). For comparison, similar experiments were carried out with human cell lines including HepG2, Caco-2, and WRL68. The efficiency of transfection (in percentage of cells) was not significantly different after transfection with lipofectin or DC-chol and comprised between 0.04 and 1.7% (extreme values) for different cultures. The efficiency of transfection decreased as the age or density of the culture increased and increased in cultures treated with EGF. Direct measurement of the rate of DNA synthesis suggested that the efficiency of transfection was related to the number of cells entering the S phase. Under the same conditions, the efficiency of transfection was one to two orders of magnitude greater in the three cell lines. A plasmid harboring 660 bp of the 5'-flanking region of CYP1A1 (containing two xenobiotic enhancer elements) fused upstream of the promoter of thymidine kinase and the CAT reporter gene was constructed. When this plasmid was transfected in human hepatocytes, CAT activity was induced as expected. We conclude that normal adult human hepatocytes can be transfected with exogenous DNA and that the transfected construct is regulated in the manner expected from in vivo studies.

Regulation of the major detoxication functions by phenobarbital and 3-methylcholanthrene in co-cultures of rat hepatocytes and liver epithelial cells

In the present study, we analysed the expression of monooxygenase activities and mRNAs associated with cytochrome P-450 (CYP), including CYP1A1/2, CYP2B1/2, CYP2C6, CYP2E1, CYP3A1/2, glutathione transferase alpha (GST alpha), aldehyde dehydrogenase and epoxide hydrolase in co-cultures of primary rat hepatocytes and rat liver epithelial cells. We observed that pentoxyresorufin O-deethylation activity was well maintained and ethoxyresorufin O-deethylation activity gradually decreased during co-culture time. In addition, we showed that phenobarbital and 3-methylcholanthrene treatments resulted in a significant increase of these activities. Two general patterns of accumulation of liver-specific mRNAs were observed. CYP1A1/2, CYP2B1/2, CYP3A1/2, GST alpha, aldehyde dehydrogenase and epoxide hydrolase mRNAs were maintained at a stable level, whereas CYP2C6 and CYP2E1 mRNAs showed a continuous decline. In addition, we observed a strong increase of CYP1A1/2 (13.6-fold) and GST alpha (3.9-fold) mRNA expression in 3-methylcholanthrene-treated co-cultures and induction of CYP2B1/2 (19-fold), CYP2C6 (10-fold), CYP3A1/2 (11.2-fold), GST alpha (9-fold), aldehyde dehydrogenase (6-fold) and epoxide hydrolase (5-fold) mRNA expression in phenobarbital-treated co-cultures. Furthermore, we demonstrated that liver-specific gene expression was restricted to hepatocytes, with the notable exception of epoxide hydrolase and CYP2E1 which were expressed in both cell types during the co-culture, as shown by the selective recovery of both hepatocytes and rat liver epithelial cells. Finally, to investigate whether co-cultures could be used to study the molecular mechanisms regulating CYP transcription, we performed transfection of hepatocytes, before the establishment of the co-culture, with large CYP2B1 (3.9 kb) or CYP2B2 (4.5 kb) promoter chloramphenicol acetyltransferase constructs or with a construct containing a 163-bp DNA sequence element reported to confer phenobarbital responsiveness. A 2-3-fold increase over the basal level of chloramphenicol acetyltransferase activity was observed in phenobarbital-treated co-cultures transfected with the phenobarbital-responsive element construct, although phenobarbital had no effect on large CYP2B1 or CYP2B2 promoter fragments. Our results demonstrate that the co-culture system provides a good tool for studying drug metabolism, and shows promise as a new tool for analysing transcriptional regulation under the influence of xenobiotics within primary hepatocytes.

Sulfotransferase gene expression in primary cultures of rat hepatocytes

Hepatocyte cultures have been used in pharmacotoxicological studies, and sulfotransferases (ST) are important drug-metabolizing enzymes in liver. The expression of sulfotransferases in hepatocyte cultures has not been examined systematically. In the present study, the mRNA levels of different sulfotransferases in male and female rat hepatocytes were examined by northern-blot analyses. Various culture conditions such as different matrices (collagen, matrigel, collagen sandwich, or co-culture with epithelial cells), medium (Way-mouth's MB 752/1 and Modified Chee's Medium) and glucocorticoid supplementation (dexamethasone, 0.1 microM) were compared. Phenol ST (ST1A1) mRNA levels decreased to about 50% of initial mRNA levels within 10 hr of culture. At 96 hr, ST1A1 mRNA levels were approximately 20% of initial values when cultured on collagen, matrigel or co-culture. The two media did not differ in ability to maintain ST1A1 mRNA levels in the absence of dexamethasone (DEX); however, DEX addition to either medium resulted in ST1A1 mRNA levels greater than 100% of the initial mRNA levels at 96 hr, with the greatest increase observed using the matrigel substratum and Chee's medium. In the absence of DEX, the mRNA levels of N-hydroxy-2-acetylaminoflurene sulfortransferase (ST1C1), estrogen sulfotransferase (ST1E2) and hydroxysteroid sulfotransferase (ST-20/21, ST-40/41, ST-60) fell to approximately 20% of their initial levels within 24 hr, and to less than 5% at 96 hr. The loss of expression of these sulfotransferases was observed with all culture conditions. Addition of DEX to the media resulted in ST-40/41 and ST-60 mRNA expression at 20 and 35% of their initial values, respectively, in cultures maintained on matrigel and Chee's medium at 96 hr. These data suggest that sulfotransferases lose their constitutive expression in hepatocyte culture, but retain their inducibility.

Perifusion of co-cultured hepatocytes: optimization of studies on drug metabolism and cytotoxicity in vitro

The combination of co-cultivation of hepatocytes and epithelial cell lines with a newly developed perifusion system was used for in vitro studies on drug metabolism and cytotoxicity. This approach improved the viability and enhanced the induction of the biotransforming capacity of the hepatocytes. As demonstrated for the induction of 7-ethoxyresorufin O-deethylase activity by 3-methylcholanthrene or benzanthracene, co-cultured hepatocytes in the perifusion system responded more sensitively to these inducers than without perifusion, most likely owing to stable (steady-state) concentrations of the inducers under the former conditions and rapidly declining concentrations under the latter conditions. The perifusion approach rendered it possible to determine the kinetics of drug metabolism during single or sequential incubations. After induction with 3-methylcholanthrene and phenobarbital, phase I metabolism of lonazolac to the monohydroxylated product in perifused co-cultures closely (87%) approached the values reported for the in vivo production, whereas in stationary co-cultures only 52% could be reached. Likewise, cytotoxic effects could be detected more precisely in the perifused co-cultures. If cells were pretreated with 0.2 mmol/L galactosamine for 3 h, perifusion with increasing concentrations of menadione differentially killed epithelial RL-ET-14 cells and hepatocytes at low and high concentrations, respectively, while in stationary co-cultures no differential effect was observed and only the higher concentrations were cytotoxic for both cells. Prevention by incubation with S-adenosylmethionine of menadione cytotoxicity up to a menadione concentration of 250 micromol/L was seen only in the perifused co-cultures, whereas in stationary cultures only a slight shift of the cytotoxic concentration exerting 50% cell damage to higher values was noted. These results demonstrate the versatile application of perifused co-cultures for studies on drug metabolism including induction of cytochrome P450-dependent enzymes and steady-state kinetics of biotransformation, as well as cytotoxic and protective effects of different drugs.

Metabolism of pimobendan in long-term human hepatocyte culture: in vivo-in vitro comparison

The aim of this study was to investigate further the potential of a new hepatocyte culture based on the hypothesis that liver cells in an appropriate in vitro environment (immobilizing gel technique) maintain high metabolic activity comparable with that in vivo. Pimobendan (UD-CG 115), a pyridazinone derivative, is a cardiotonic vasodilator that increases myocardial contractility through calcium sensitization and relaxation of vascular smooth muscle, probably due to phosphodiesterase inhibition. In man, pimobendan is O-demethylated to UD-CG 212. This latter is metabolized to O- and N-glucuronides. Pimobendan itself is also glucuronidated to a N-glucuronide. Human hepatocytes immobilized in collagen gel were incubated with pimobendan to investigate their metabolic activity in the long-term and to compare the results to the data from clinical trials. 14C-labelled pimobendan was incubated at two concentrations (10 and 100 microM) at day 3, 11 and 22 of culture, and samples were analysed after 4, 24 and 48-h incubation. Metabolic patterns were evaluated by hplc with radioactivity-, diode array-, and mass spectral-detection. In vitro, pimobendan was O-demethylated and subsequently O-glucuronidated. The rate of metabolism of pimobendan could be maintained in this culture system for > 3 weeks. However, the relative amount of a putative N-glucuronide under in vitro conditions was lower than in vivo.

A specific microassay for evaluating hepatic LDH activity in co-cultures of hepatocytes with other cells

This study describes the development of a simple, rapid and reproducible microassay for determining the intracellular LDH activity of rat hepatocytes present in a co-culture system with other cells. The procedure involves treatment of cellular homogenates with an anti-LDH antiserum that specifically inhibits the LDH activity of rat hepatocytes. The assay is performed in 96-well plates and LDH activity can be measured directly in the same wells using a colorimetric method. The difference in LDH activity values measured before and after antiserum incubation reflects the LDH content of the hepatocytes in the sample. The advantages of this method are the small number of cells required, a reduction in sample handling and the possibility of differentiating LDH activity in hepatic and non-hepatic cells. The possible applications of this technique as a parameter for biochemical data and as a test for cytotoxicity studies in co-cultures are also discussed.