Long-term primary cultures of adult human hepatocytes

Perfluoropolyether-Based Gut-Liver-on-a-Chip for the Evaluation of First-Pass Metabolism and Oral Bioavailability of Drugs

In the evolving field of drug discovery and development, multiorgans-on-a-chip and microphysiological systems are gaining popularity owing to their ability to emulate in vivo biological environments. Among the various gut-liver-on-a-chip systems for studying oral drug absorption, the chip developed in this study stands out with two distinct features: incorporation of perfluoropolyether (PFPE) to effectively mitigate drug sorption and a unique enterohepatic single-passage system, which simplifies the analysis of first-pass metabolism and oral bioavailability. By introducing a bolus drug injection into the liver compartment, hepatic extraction alone could be evaluated, further enhancing our estimation of intestinal availability. In a study on midazolam (MDZ), PFPE-based chips showed more than 20-times the appearance of intact MDZ in the liver compartment effluent compared to PDMS-based counterparts. Notably, saturation of hepatic metabolism at higher concentrations was confirmed by observations when the dose was reduced from 200 μM to 10 μM. This result was further emphasized when the metabolism was significantly inhibited by the coadministration of ketoconazole. Our chip, which is designed to minimize the dead volume between the gut and liver compartments, is adept at sensitively observing the saturation of metabolism and the effect of inhibitors. Using genome-edited CYP3A4/UGT1A1-expressing Caco-2 cells, the estimates for intestinal and hepatic availabilities were 0.96 and 0.82, respectively; these values are higher than the known human in vivo values. Although the metabolic activity in each compartment can be further improved, this gut-liver-on-a-chip can not only be used to evaluate oral bioavailability but also to carry out individual assessment of both intestinal and hepatic availability.

A functional long-term 2D serum-free human hepatic in vitro system for drug evaluation

Human in vitro hepatic models generate faster drug toxicity data with higher human predictability compared to animal models. However, for long-term studies, current models require the use of serum and 3D architecture, limiting their utility. Maintaining a functional long-term human in vitro hepatic culture that avoids complex structures and serum would improve the value of such systems for preclinical studies. This would also enable a more straightforward integration with current multi-organ devices to study human systemic toxicity to generate an alternative model to chronic animal evaluations. A human primary hepatocyte culture system was characterized for 28 days in 2D and serum-free defined conditions. Under the studied conditions, human primary hepatocytes maintained their characteristic morphology, hepatic markers and functions for 28 days. The acute and chronic administration of known drugs validated the sensitivity of the system for drug testing. This human 2D model represents a realistic system to evaluate hepatic function for long-term drug studies, without the need of animal serum, confounding variable in most models, and with less complexity and resultant cost compared to most 3D models. The defined culture conditions can easily be integrated into complex multi-organ in vitro models for studying systemic effects driven by the liver function for long-term evaluations.

HepaChip-MP - a twenty-four chamber microplate for a continuously perfused liver coculture model

HepaChip microplate (HepaChip-MP) is a microfluidic platform comprised of 24 independent culture chambers with continuous, unidirectional perfusion. In the HepaChip-MP, an automated dielectrophoresis process selectively assembles viable cells into elongated micro tissues. Freshly isolated primary human hepatocytes (PHH) and primary human liver endothelial cells (HuLEC) were successfully assembled as cocultures aiming to mimic the liver sinusoid. Minimal quantities of primary human cells are required to establish micro tissues in the HepaChip-MP. Metabolic function including induction of CYP enzymes in PHH was successfully measured demonstrating a high degree of metabolic activity of cells in HepaChip-MP cultures and sufficient sensitivity of LC-MS analysis even for the relatively small number of cells per chamber. Further, parallelization realized in HepaChip-MP enabled the acquisition of dose-response toxicity data of diclofenac with a single device. Several unique technical features should enable a widespread application of this in vitro model. We have demonstrated fully automated preparation of cell cultures in HepaChip-MP using a pipetting robot. The tubeless unidirectional perfusion system based on gravity-driven flow can be operated within a standard incubator system. Overall, the system readily integrates in workflows common in cell culture labs. Further research will be directed towards optimization of media composition to further extend culture lifetime and study oxygen gradients and their effect on zonation within the sinusoid-like microorgans. In summary, we have established a novel parallelized and scalable microfluidic in vitro liver model showing hepatocyte function and anticipate future in-depth studies of liver biology and applications in pre-clinical drug development.

La plasticidad del hepatocito y su relevancia en la fisiología y la patología hepática

El hígado es uno de los principales órganos encargados de mantener la homeostasis en vertebrados,  además de poseer una gran capacidad regenerativa. El hígado está constituido por diversos tipos celulares que de forma coordinada contribuyen para que el órgano funcione eficientemente. Los hepatocitos representan el tipo celular principal de este órgano y llevan a cabo la mayoría de sus actividades; además, constituyen una población heterogénea de células epiteliales con funciones especializadas en el metabolismo. El fenotipo de los hepatocitos está controlado por diferentes vías de señalización, como la vía del TGFβ/Smads, la ruta Hippo/YAP-TAZ y la vía Wnt/β-catenina, entre otras. Los hepatocitos son células que se encuentran normalmente en un estado quiescente, aunque cuentan con una plasticidad intrínseca que se manifiesta en respuesta a diversos daños en el hígado; así, estas células reactivan su capacidad proliferativa o cambian su fenotipo a través de procesos celulares como la transdiferenciación o la transformación, para contribuir a mantener la homeostasis del órgano en condiciones saludables o desarrollar diversas  patologías.

Humanized Mice Are Instrumental to the Study of Plasmodium falciparum Infection

Research using humanized mice has advanced our knowledge and understanding of human haematopoiesis, non-adaptive and adaptive immunity, autoimmunity, infectious disease, cancer biology, and regenerative medicine. Challenges posed by the human-malaria parasite Plasmodium falciparum include its complex life cycle, the evolution of drug resistance against anti-malarials, poor diagnosis, and a lack of effective vaccines. Advancements in genetically engineered and immunodeficient mouse strains, have allowed for studies of the asexual blood stage, exoerythrocytic stage and the transition from liver-to-blood stage infection, in a single vertebrate host. This review discusses the process of "humanization" of various immunodeficient/transgenic strains and their contribution to translational biomedical research. Our work reviews the strategies employed to overcome the remaining-limitations of the developed human-mouse chimera(s).

Self-contained, low-cost Body-on-a-Chip systems for drug development

Integrated multi-organ microphysiological systems are an evolving tool for preclinical evaluation of the potential toxicity and efficacy of drug candidates. Such systems, also known as Body-on-a-Chip devices, have a great potential to increase the successful conversion of drug candidates entering clinical trials into approved drugs. Systems, to be attractive for commercial adoption, need to be inexpensive, easy to operate, and give reproducible results. Further, the ability to measure functional responses, such as electrical activity, force generation, and barrier integrity of organ surrogates, enhances the ability to monitor response to drugs. The ability to operate a system for significant periods of time (up to 28 d) will provide potential to estimate chronic as well as acute responses of the human body. Here we review progress towards a self-contained low-cost microphysiological system with functional measurements of physiological responses. Impact statement Multi-organ microphysiological systems are promising devices to improve the drug development process. The development of a pumpless system represents the ability to build multi-organ systems that are of low cost, high reliability, and self-contained. These features, coupled with the ability to measure electrical and mechanical response in addition to chemical or metabolic changes, provides an attractive system for incorporation into the drug development process. This will be the most complete review of the pumpless platform with recirculation yet written.

Determination of Functional Activity of Human iPSC-Derived Hepatocytes by Measurement of CYP Metabolism

The advent of induced pluripotent stem cell (iPSC) technology has enabled the modeling of an array of specific human disease phenotypes, aiding in the increasingly important and indispensable understanding of disease progression and pathogenesis. Pluripotent stem cell-derived hepatocytes present a new avenue for drug screening and personalized drug testing toward precision medicine. CYP450 microsomal enzymes play a critical role in drug metabolism. Hence, CYP activity measurement of iPSC-derived hepatocytes is a vital prerequisite, to ensure metabolic functionality before proceeding to drug testing. Herein, we describe the protocol for measurement of different CYP450 enzyme activities in human iPSC-derived hepatocytes.

Opportunities and challenges in using human hepatocytes in cytochromes P450 induction assays

INTRODUCTION

Identification of inducers of xenobiotic-metabolizing cytochromes P450 (CYP) is of topical interest. The issue mainly concerns three sectors: (i) preclinical testing of drug candidates and testing existing drugs and their combinations; (ii) food safety applications with regard to additives, contaminants, and adulterants; (iii) environmental applications, comprising detection and identification of endocrine disruptors.

AREAS COVERED

A literature search was performed using the PubMed database, covering state-of-the-art of human hepatocyte (HH) culture use, and their exploitation for the identification of P450 inducers. A list of CYP inducers identified by HHs is provided.

EXPERT OPINION

Primary cultures of HHs had long been considered as a gold standard for induction assays of xenobiotic-metabolizing enzymes. Owing to several shortcomings of HHs, alternative approaches such as immortalization of HHs, use of cell lines, generation of clonal cell lines from HHs, use of induced pluripotent stem (iPS) cells, cells from humanized animals, etc., were employed. While yielding particular advantage, overall, alternatives to HHs still remain an avenue for discrete applications or technical situations. Thus, HHs remain the most suitable model for complex CYP induction studies. The summary may be effectively expressed by strength/weakness/opportunity/threats analysis.

Synergistic activation of human pregnane X receptor by binary cocktails of pharmaceutical and environmental compounds

Humans are chronically exposed to multiple exogenous substances, including environmental pollutants, drugs and dietary components. Many of these compounds are suspected to impact human health, and their combination in complex mixtures could exacerbate their harmful effects. Here we demonstrate that a pharmaceutical oestrogen and a persistent organochlorine pesticide, both exhibiting low efficacy when studied separately, cooperatively bind to the pregnane X receptor, leading to synergistic activation. Biophysical analysis shows that each ligand enhances the binding affinity of the other, so the binary mixture induces a substantial biological response at doses at which each chemical individually is inactive. High-resolution crystal structures reveal the structural basis for the observed cooperativity. Our results suggest that the formation of ‘supramolecular ligands' within the ligand-binding pocket of nuclear receptors contributes to the synergistic toxic effect of chemical mixtures, which may have broad implications for the fields of endocrine disruption, toxicology and chemical risk assessment.

Endocrine-disrupting chemicals act on nuclear hormone receptors, such as PXR. Here, Delfosse et al. show how two such chemicals interact with each other in the PXR ligand-binding pocket, forming a so-called supramolecular ligand that is a more potent PXR activator than each of the two chemicals alone.

Cold Preservation of Human Adult Hepatocytes for Liver Cell Therapy

Hepatocyte transplantation is a promising alternative therapy for the treatment of hepatic failure, hepatocellular deficiency, and genetic metabolic disorders. Hypothermic preservation of isolated human hepatocytes is potentially a simple and convenient strategy to provide on-demand hepatocytes in sufficient quantity and of the quality required for biotherapy. In this study, first we assessed how cold storage in three clinically safe preservative solutions (UW, HTS-FRS, and IGL-1) affects the viability and in vitro functionality of human hepatocytes. Then we evaluated whether such cold-preserved human hepatocytes could engraft and repopulate damaged livers in a mouse model of liver failure. Human hepatocytes showed comparable viabilities after cold preservation in the three solutions. The ability of fresh and cold-stored hepatocytes to attach to a collagen substratum and to synthesize and secrete albumin, coagulation factor VII, and urea in the medium after 3 days in culture was also equally preserved. Cold-stored hepatocytes were then transplanted in the spleen of immunodeficient mice previously infected with adenoviruses containing a thymidine kinase construct and treated with a single dose of ganciclovir to induce liver injury. Engraftment and liver repopulation were monitored over time by measuring the blood level of human albumin and by assessing the expression of specific human hepatic mRNAs and proteins in the recipient livers by RT-PCR and immunohistochemistry, respectively. Our findings show that cold-stored human hepatocytes in IGL-1 and HTS-FRS preservative solutions can survive, engraft, and proliferate in a damaged mouse liver. These results demonstrate the usefulness of human hepatocyte hypothermic preservation for cell transplantation.

The WNT/β-catenin pathway is a transcriptional regulator of CYP2E1, CYP1A2, and aryl hydrocarbon receptor gene expression in primary human hepatocytes

The wingless-type MMTV integration site family (WNT)/β-catenin/adenomatous polyposis coli (CTNNB1/APC) pathway has been identified as a regulator of drug-metabolizing enzymes in the rodent liver. Conversely, little is known about the role of this pathway in drug metabolism regulation in human liver. Primary human hepatocytes (PHHs), which are the most physiologically relevant culture system to study drug metabolism in vitro, were used to investigate this issue. This study assessed the link between cytochrome P450 expression and WNT/β-catenin pathway activity in PHHs by modulating its activity with recombinant mouse Wnt3a (the canonical activator), inhibitors of glycogen synthase kinase 3β, and small-interfering RNA to invalidate CTNNB1 or its repressor APC, used separately or in combination. We found that the WNT/β-catenin pathway can be activated in PHHs, as assessed by universal β-catenin target gene expression, leucine-rich repeat containing G protein-coupled receptor 5. Moreover, WNT/β-catenin pathway activation induces the expression of CYP2E1, CYP1A2, and aryl hydrocarbon receptor, but not of CYP3A4, hepatocyte nuclear factor-4α, or pregnane X receptor (PXR) in PHHs. Specifically, we show for the first time that CYP2E1 is transcriptionally regulated by the WNT/β-catenin pathway. Moreover, CYP2E1 induction was accompanied by an increase in its metabolic activity, as indicated by the increased production of 6-OH-chlorzoxazone and by glutathione depletion after incubation with high doses of acetaminophen. In conclusion, the WNT/β-catenin pathway is functional in PHHs, and its induction in PHHs represents a powerful tool to evaluate the hepatotoxicity of drugs that are metabolized by CYP2E1.

Stem Cell Strategies to Evaluate Idiosyncratic Drug-induced Liver Injury

The host-dependent nature of idiosyncratic drug-induced liver injury (iDILI) suggests that rare genetic polymorphisms may contribute to the disease. Indeed, a few mutations in key genes have already been identified using conventional human genetics approaches. Over 50 commonly used drugs can precipitate iDILI, making this a substantial medical problem. Only recently have human induced pluripotent stem cells been used as a research tool to discover novel iDILI genes and to study the mechanisms of iDILI in vitro. Here we review the current state of stem cell use in the investigation of iDILI, with a special focus on genetics. In addition, the concerns and difficulties associated with genetics and animal model research are discussed. We then present the features of patient-specific pluripotent stem cells (which may be derived from iDILI patients themselves), and explain why these cells may be of great utility. A variety of recent approaches to produce hepatocyte-like cells from pluripotent cells and the associated advantages and limitations of such cells are discussed. Future directions for the use of stem cell science to investigate iDILI include novel ways to identify new iDILI genes, a consideration of epigenetic impacts on iDILI, and the development of new and improved strategies for the production of hepatocytes from human pluripotent cells.

Study of Protoscolicidal Effects of Hypertonic Glucose on Protoscolices of Hydatid Cyst at Different Concentrations and Exposure Times

Surgical operation is the treatment of choice for hydatid cyst. To date, many protoscolicidal substances have been used for inactivation of hydatid cyst contents but most of these compounds may produce several side effects. The aim of this study was to evaluate the protoscolicidal effects of hypertonic glucose on protoscolices of hydatid cyst at different concentrations and exposure times. Protoscolices were obtained aseptically from the livers of slaughtered sheep at Qazvin abattoir, Iran. Protoscolices were exposed to different concentrations of hypertonic glucose (10%, 15%, 20%, 25%, 30%, 40%, and 50%) at different times (1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 20, 30, 40, 50, and 60 min). Viability of protoscolices was evaluated by 0.1% eosin and the movement of protoscolices flame cells. The highest protoscolicidal effect (100%) of hypertonic glucose was obtained at concentrations 40% and 50% following 40 and 20 min exposure times, respectively. Some protoscolicidal agents show a variety of dangerous complications such as biliary tract fibrosis and liver necrosis; however, hypertonic glucose especially at a concentration of 40% may demonstrate less side effects compared with glucose 50%. Further in vivo investigations are suggested.

Human induced pluripotent stem cells in hepatology: beyond the proof of concept

The discovery of the wide plasticity of most cell types means that it is now possible to produce virtually any cell type in vitro. This concept, developed because of the possibility of reprogramming somatic cells toward induced pluripotent stem cells, provides the opportunity to produce specialized cells that harbor multiple phenotypical traits, thus integrating genetic interindividual variability. The field of hepatology has exploited this concept, and hepatocyte-like cells can now be differentiated from induced pluripotent stem cells. This review discusses the choice of somatic cells to be reprogrammed by emergent new and nonintegrative strategies, as well as the application of differentiated human induced pluripotent stem cells in hepatology, including liver development, disease modeling, host-pathogen interactions, and drug metabolism and toxicity. The actual consensus is that hepatocyte-like cells generated in vitro present an immature phenotype. Currently, developed strategies used to resolve this problem, such as overexpression of transcription factors, mimicking liver neonatal and postnatal modifications, and re-creating the three-dimensional hepatocyte environment in vitro and in vivo, are also discussed.

Ex vivo magnetic resonance imaging of transplanted hepatocytes in a rat model of acute liver failure

Hepatocyte transplantation is being evaluated as an alternative to liver transplantation. However, the fate of hepatocytes after transplantation is not well defined. The aims of the study were to improve hepatocyte labeling in vitro using superparamagnetic iron oxide nanoparticles (SPIOs) and to perform in vivo experiments on tracking labeled cells by magnetic resonance imaging (MRI). Human and rat hepatocytes were labeled in vitro for 16 h with clinically approved SPIOs (12.5 µg Fe/ml) and protamine sulfate (3 µg/ml) as a transfection agent. Increased cellular iron uptake was obtained, and cell viability and function were shown not to be affected by labeling. Labeled cells (2,000/µl) could be detected on T2-weighted images in vitro using a 7T MR scanner. In a rat model of acute liver failure (ALF), female recipients received intrasplenic transplantation of 2 × 10(7) male rat hepatocytes 28-30 h after intraperitoneal injection of d-galactosamine (1.2 g/kg). There were four groups (n = 4 each): vehicle injection, injection of freshly isolated cells labeled with CM-DiI, injection of cultured cells labeled with CM-DiI, and injection of cultured cells labeled with both SPIOs and CM-DiI. Ex vivo T2*-weighted gradient-echo images at 7T MRI were acquired at day 7 post-ALF induction. Six days after transplantation, SPIOs were detected in the rat liver as a decrease in the MRI signal intensity in the surviving animals. Histologically, most of the SPIOs were located in Kupffer cells, indicating clearance of labeled hepatocytes. Furthermore, labeled cells could not be detected in the liver by the fluorescent dye or by PCR for the Y-chromosome (Sry-2 gene). In conclusion, optimum conditions to label human hepatocytes with SPIOs were established and did not affect cell viability or metabolic function and were sufficient for in vitro MRI detection. However, the clearance of hepatocytes after transplantation limits the value of MRI for assessing long-term hepatocyte engraftment.

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.

The new murine hepatic 3A cell line responds to stress stimuli by activating an efficient Unfolded Protein Response (UPR)

In the present study we have investigated the properties of a novel cell line (3A cells) obtained from the liver of 14.5 days post coitum (dpc) wild-type mouse embryo. 3A cells morphology was characterized by fluorescent localization of F-actin and β-catenin. The expression of specific genes and proteins essential to liver function in these cells was comparable or even more efficient then in the differentiated hepatocytic cell line MMH-D6. 3A cells also showed the capability to excrete molecules in extracellular spaces resembling functional bile canaliculi, glycogen storage activity and the ability to control retinol-binding protein 4 secretion in response to retinol deprivation. Their response to the exogenous stress stimulus induced by tunicamycin was analysed by PCR Pathway Array containing 84 genes involved in the Unfolded Protein Response (UPR). 3A cells were shown to activate the UPR following a typical stressful event, indicating that this cellular model could be further exploited to investigate hepatic proteins secretion and specific reaction to different injuries.

Modular bioreactor for primary human hepatocyte culture: medium flow stimulates expression and activity of detoxification genes

Down-regulation of detoxification genes, notably cytochrome P450 (CYPs), in primary hepatocyte cultures is a long-standing and major concern. We evaluated the influence of medium flow in this model. Hepatocytes isolated from 12 different liver donors were cultured either in a multichamber modular bioreactor (MCmB, flow rate 250-500 μL/min) or under standard/static conditions, and the expression of 32 genes, enzyme activities and biological parameters were measured 7-21 days later. mRNA expression of genes involved in xenobiotic/drug metabolism and transport, including CYP1A1, 1A2, 2B6, 2C9, 3A4 (and activities for some of them), UDP-glucuronosyltransferase (UGT) 1A1, UGT2B4, UGT2B7, glutathione S-transferase (GSTα), and multidrug resistance protein 1 (MDR1) and MRP2, were specifically up-regulated by medium flow as compared with static controls in all cultures tested. In 2-week-old cultures, expression of detoxification genes reached levels close to or higher than those measured in freshly isolated hepatocytes. In contrast, CYP2D6 and most of other tested genes were not affected by medium flow. We conclude that medium flow specifically interferes with, and up-regulates, the activity of xenosensors and/or the expression of detoxification genes in primary human hepatocytes. Down-regulation of detoxification genes in conventional (static) cultures is therefore partly a consequence of the absence of medium circulation.

Use of a clinically approved iron oxide MRI contrast agent to label human hepatocytes

Reliable noninvasive methods are needed to monitor cell engraftment and graft survival after hepatocyte transplantation. Superparamagnetic iron oxide nanoparticles (SPIOs) have been shown to accumulate in various types of cells, and are currently the labeling agent of choice for cellular magnetic resonance imaging (MRI). However, for successful clinical translation to hepatocyte transplantation, it is important that hepatocytes maintain their viability and synthetic function after labeling. In this study, primary human hepatocytes were incubated with increasing concentrations of clinical grade SPIOs for different time intervals. SPIOs uptake was confirmed by light and fluorescence microscopy, and intracellular iron content quantified by a colorimetric ferrozine-based assay. Studies were performed to determine if labeling affected cell viability and function. Intracellular iron concentrations increased in a time- and dose-dependent manner after incubation with SPIOs. Labeling had minimal short-term effects on cell attachment and mitochondrial function. However, exposure of hepatocytes to SPIOs resulted in a dose- and time-dependent reduction in protein synthesis. Cell labeling for 16 h had no significant effect on hepatocyte-specific function, but longer periods of incubation resulted in a dose-dependent decrease in albumin production. Hepatocytes incorporated SPIOs at sufficient levels for in vitro detection on a 7-T MRI imaging system, with a minimum of 2,000 SPIO-labeled cells/μl detected by a decreased T2 relaxivity compared to controls. Intrasplenic transplantation of human hepatocytes labeled with 50 μg Fe/ml of SPIOs was performed in nonobese diabetic/severe combined immune deficiency (NOD-Scid) mice. Recipient livers showed a clear decrease in signal intensity on T2*-weighted MR images when compared to controls, allowing detection of hepatocytes. With further experiments to optimize the conditions for labeling human hepatocytes, it should be possible to apply this technique to track hepatocyte transplantation in patients with liver disease.

General review on in vitro hepatocyte models and their applications

In vitro hepatocyte models represent very useful systems in both fundamental research and various application areas. Primary hepatocytes appear as the closest model for the liver in vivo. However, they are phenotypically unstable, have a limited life span and in addition, exhibit large interdonor variability when of human origin. Hepatoma cell lines appear as an alternative but only the HepaRG cell line exhibits various functions, including major cytochrome P450 activities, at levels close to those found in primary hepatocytes. In vitro hepatocyte models have brought a substantial contribution to the understanding of the biochemistry, physiology, and cell biology of the normal and diseased liver and in various application domains such as xenobiotic metabolism and toxicity, virology, parasitology, and more generally cell therapies. In the future, new well-differentiated hepatocyte cell lines derived from tumors or from either embryonic or adult stem cells might be expected and although hepatocytes will continue to be used in various fields, these in vitro liver models should allow marked advances, especially in cell-based therapies and predictive and mechanistic hepatotoxicity of new drugs and other chemicals. All models will benefit from new developments in throughput screening based on cell chips coupled with high-content imaging and in toxicogenomics technologies.

Sandwich-cultured hepatocytes: an in vitro model to evaluate hepatobiliary transporter-based drug interactions and hepatotoxicity

Sandwich-cultured hepatocytes (SCH) are a powerful in vitro tool that can be utilized to study hepatobiliary drug transport, species differences in drug transport, transport protein regulation, drug-drug interactions, and hepatotoxicity. This review provides an up-to-date summary of the SCH model, including a brief history of, and introduction to, the use of SCH, as well as methodology to evaluate hepatobiliary drug disposition. A summary of the literature that has utilized this model to examine the interplay between drug-metabolizing enzymes and transport proteins, drug-drug interactions at the transport level, and hepatotoxicity as a result of altered hepatic transport also is provided.

Use of human hepatocytes to investigate blood coagulation factor

Coagulation is the complex process by which activation of plasmatic haemostasis proteins ends up with the generation of fibrin. Most of the plasma coagulation proteins are synthesized in hepatocytes. The aim of this chapter is to describe experimental procedures allowing to measure the secretion by primary human hepatocytes and functional activity (including production of fibrillar material from extracellular medium) of haemostasis proteins including factors II, V, VII, VIII, PIVKA-II (protein induced by vitK 1 absence or antagonist II), antithrombin and protein S. In addition, we show how treatments of hepatocyte cultures with vitamin K and/or warfarin affect the secretion of haemostasis proteins. The results demonstrate that primary cultures of human hepatocytes constitute an invaluable model for investigating haemostasis protein expression and activity and therapeutic strategies targeting these proteins.

Chimeric mice with humanized liver: tools for the study of drug metabolism, excretion, and toxicity

Recent developments in animal models have allowed the creation of mice with genetic alterations that cause hepatocyte damage that results, over time, in the loss of native hepatocytes. If donor, human hepatocytes are transplanted into these animals, they repopulate the host liver, frequently replacing over 70% of the native liver with human cells. Immunodeficient mice that overexpress urokinase-type plasminogen activator (uPA) and, alternatively, with a knockout of the fumarylacetoacetate hydrolase (Fah) genes are the two most common mouse models for these studies. These mice are called chimeric or "humanized" because the liver is now partially repopulated with human cells. In this report we will review the published work with respect to Phase I and Phase II metabolic pathways and the expression of hepatic transport proteins. While the studies are still at the descriptive stage, it is already clear that some humanized mice display high levels of repopulation with human hepatocytes, express basal and inducible human CYP450 genes, and human conjugation and hepatic transport pathways. When the strengths and weaknesses of these humanized mouse models are fully understood, they will likely be quite valuable for investigations of human liver-mediated metabolism and excretion of drugs and xenobiotics, drug-drug interactions, and for short- and long-term investigation of the toxicity of drugs or chemicals with significant human exposure.

Isolation and culture of primary hepatocytes from resected human liver tissue

As our knowledge of the species differences in drug metabolism and drug-induced hepatotoxicity has expanded significantly, the need for human-relevant in vitro hepatic model systems has become more apparent than ever before. Human hepatocytes have become the "gold standard" for evaluating hepatic metabolism and toxicity of drugs and other xenobiotics in vitro. In addition, they are becoming utilized more extensively for many kinds of biomedical research, including a variety of biological, pharmacological, and toxicological studies. This chapter describes methods for the isolation of primary human hepatocytes from liver tissue obtained from an encapsulated end wedge removed from patients undergoing resection for removal of liver tumors or from resected segments from whole livers obtained from multi-organ donors. In addition, methods are described for culturing primary hepatocytes under various matrix compositions and geometries, which reestablish intercellular contacts and normal cellular architecture for optimal phenotypic gene expression and response to drugs and other xenobiotics in vitro. Overall, improved isolation, cultivation, and preservation methods have expanded the number of applications for primary human hepatocytes in basic research, which has allowed for exciting advances in our understanding of the biochemical and molecular mechanisms of human liver toxicity and disease.

Hepatocyte differentiation

Increasingly, research suggests that for certain systems, animal models are insufficient for human toxicology testing. The development of robust, in vitro models of human toxicity is required to decrease our dependence on potentially misleading in vivo animal studies. A critical development in human toxicology testing is the use of human primary hepatocytes to model processes that occur in the intact liver. However, in order to serve as an appropriate model, primary hepatocytes must be maintained in such a way that they persist in their differentiated state. While many hepatocyte culture methods exist, the two-dimensional collagen "sandwich" system combined with a serum-free medium, supplemented with physiological glucocorticoid concentrations, appears to robustly maintain hepatocyte character. Studies in rat and human hepatocytes have shown that when cultured under these conditions, hepatocytes maintain many markers of differentiation including morphology, expression of plasma proteins, hepatic nuclear factors, phase I and II metabolic enzymes. Functionally, these culture conditions also preserve hepatic stress response pathways, such as the SAPK and MAPK pathways, as well as prototypical xenobiotic induction responses. This chapter will briefly review culture methodologies but will primarily focus on hallmark hepatocyte structural, expression and functional markers that characterize the differentiation status of the hepatocyte.

Effects of dinuclear copper(II) complexes with 6-(benzylamino)purine derivatives on AhR and PXR dependent expression of cytochromes P450 CYP1A2 and CYP3A4 genes in primary cultures of human hepatocytes

A series of dinuclear copper(II) complexes of the compositions [Cu(2)(micro-L(n))(2)(micro-Cl)(2)Cl(2)] (1, 2), [Cu(2)(micro-L(n))(4)Cl(2)]Cl(2).2H(2)O (3, 4) and [Cu(2)(micro-L(n))(4)(ClO(4))(2)](ClO(4))(2).xSolv (5, 6; xSolv=4MeOH for 5 and 2EtOH for 6), involving 6-(benzylamino)purine derivatives (L(n)), have been evaluated with the aim to determine their possible drug interactions and their capability to induce the expression of major drug-metabolizing cytochromes P450. The above-mentioned complexes have been chosen based on the fact that substantial both in vitro (cytotoxicity, SOD-mimic) and in vivo (antidiabetic) biological activity has been found for them. As models, primary cultures of human hepatocytes and human hepatoma cells HepG2 transiently transfected with a plasmid containing dioxin-responsive element fused to the luciferase reporter gene (DRE-LUC) have been chosen. It has been found that the tested complexes 1-6 did not significantly induce the expression of CYP1A2 and CYP3A4 mRNAs in the concentration range of 0.1-10.0microM, in three different primary human hepatocyte cultures after 24h of the treatment. On the other hand, the model inducers, i.e. 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD) and rifampicin, significantly increased the levels of CYP1A2 and CYP3A4 mRNAs in all cultures. In addition, compounds 1-6 did not transactivate DRE-LUC in transiently transfected HepG2, while TCDD strongly induced luciferase activity after 24h of incubation. Based on the obtained results, it may be concluded that the studied dinuclear copper(II) complexes 1-6 possess very low toxicological potential to cause drug interactions in terms of transcriptional activation of the major human cytochromes P450.

Liver tissue engineering in the evaluation of drug safety

Assessment of drug-liver interactions is an integral part of predicting the safety profile of new drugs. Existing model systems range from in vitro cell culture models to FDA-mandated animal tests. Data from these models often fail, however, to predict human liver toxicity, resulting in costly failures of clinical trials. In vitro screens based on cultured hepatocytes are now commonly used in early stages of development, but many toxic responses in vivo seem to be mediated by a complex interplay among several different cell types. We discuss some of the evolving trends in liver cell culture systems applied to drug safety assessment and describe an experimental model that captures complex liver physiology through incorporation of heterotypic cell-cell interactions, 3D architecture and perfused flow. We demonstrate how heterotypic interactions in this system can be manipulated to recreate an inflammatory environment and apply the model to test compounds that potentially exhibit idiosyncratic drug toxicity. Finally, we provide a perspective on how the range of existing and emerging in vitro liver culture approaches, from simple to complex, might serve needs across the range of stages in drug discovery and development, including applications in molecular therapeutics.

Ascorbic acid combats arsenic-induced oxidative stress in mice liver

Repeated injections of arsenic trioxide induced oxidative stress and hepatotoxicity in mice as revealed from elevated levels of glutamate oxaloacetate transaminases, glutamate pyruvate transaminases, acid and alkaline phosphatases, lipid peroxidation along with reduction of superoxide dismutase, catalase, reduced glutathione content, glutathione reductase and succinate dehydrogenase activities. The present investigation was undertaken to test whether simultaneous feeding of vitamin C can combat hepatotoxicity in arsenic intoxicated mice. Hepatoprotective potential of vitamin C was indicated by its ability to restore GSH, SOD, CAT, AcP, AlkP and GRD levels towards near normal. Electron microscopic studies further supported the biochemical findings confirming the hepatoprotective potential of ascorbic acid. Besides, cytogenetical endpoints (chromosome aberrations, micronuclei, mitotic index and sperm head anomaly) were also analyzed. Administration of vitamin C alone did not show any sign of toxicity of its own. Based on the present findings, ascorbic acid appears to have protective effects against arsenic toxicity and oxidative stress.

Evolving concepts in liver tissue modeling and implications for in vitro toxicology

The development of human cell models stably expressing functional properties of the in vivo cells they are derived from for predicting toxicity of chemicals is a major challenge. For mimicking the liver, a major target of toxic chemicals, primary hepatocytes represent the most pertinent model. Their use is limited by interdonor functional variability and early phenotypic changes although their lifespan can be extended not only by culturing in a 2D dimension under sophisticated conditions but also by the use of synthetic and natural scaffolds as 3D supporting templates that allow cells to have a more stable microenvironment. Hepatocytes derived from stem cells could be the most appropriate alternative but up to now only liver progenitors/hepatoblasts are obtained in vitro. A few hepatocyte cell lines have retained a variable set of liver-specific functions. Among them are the human hepatoma HepaRG cells that express drug metabolism capacity at levels close to those found in primary hepatocytes making them a suitable model for both acute and chronic toxicity studies. New screening strategies are now proposed based on miniaturized and automated systems; they include the use of microfluidic chips and cell chips coupled with high content imaging analysis. Toxicogenomics technologies (particularly toxicotranscriptomics) have emerged as promising in vitro approaches for better identification and discrimination of cellular responses to chemicals. They should allow to discriminate compounds on the basis of the identification of a set of markers and/specific signaling pathways.

Induction of hepatic cytochrome P450 enzymes: methods, mechanisms, recommendations, and in vitro-in vivo correlations

Induction of drug-clearance pathways (Phase 1 and 2 enzymes and transporters) can have important clinical consequences. Inducers can (1) increase the clearance of other drugs, resulting in a decreased therapeutic effect, (2) increase the activation of pro-drugs, causing an alteration in their efficacy and pharmacokinetics, and (3) increase the bioactivation of drugs that contribute to hepatotoxicity via reactive intermediates. Nuclear receptors are key mediators of drug-induced changes in the expression of drug-clearance pathways. However, species differences in nuclear receptor activation make the prediction of cytochrome P450 (CYP) induction in humans from data derived from animal models problematic. Thus, in vitro human-relevant model systems are increasingly used to evaluate enzyme induction. In this review, the authors' current understanding of the mechanisms of enzyme induction and the in vitro methods for assessing the induction potential of new drugs will be discussed. Relevant issues and considerations surrounding proper study design and the interpretation of in vitro results will be discussed in light of the current US Food and Drug Administration (FDA) recommendations.

Serum-derived hepatitis C virus infection of primary human hepatocytes is tetraspanin CD81 dependent

Hepatitis C virus-positive serum (HCVser, genotypes 1a to 3a) or HCV cell culture (JFH1/HCVcc) infection of primary normal human hepatocytes was assessed by measuring intracellular HCV RNA strands. Anti-CD81 antibodies and siRNA-CD81 silencing markedly inhibited (>90%) HCVser infection irrespective of HCV genotype, viral load, or liver donor, while hCD81-large intracellular loop (LEL) had no effect. However, JFH1/HCVcc infection of hepatocytes was modestly inhibited (40 to 60%) by both hCD81-LEL and anti-CD81 antibodies. In conclusion, CD81 is involved in HCVser infection of human hepatocytes, and comparative studies of HCVser versus JFH1/HCVcc infection of human hepatocytes and Huh-7.5 cells revealed that the cell-virion combination is determinant of the entry process.

Primary hepatocytes: current understanding of the regulation of metabolic enzymes and transporter proteins, and pharmaceutical practice for the use of hepatocytes in metabolism, enzyme induction, transporter, clearance, and hepatotoxicity studies

This review brings you up-to-date with the hepatocyte research on: 1) in vitro-in vivo correlations of metabolism and clearance; 2) CYP enzyme induction, regulation, and cross-talk using human hepatocytes and hepatocyte-like cell lines; 3) the function and regulation of hepatic transporters and models used to elucidate their role in drug clearance; 4) mechanisms and examples of idiosyncratic and intrinsic hepatotoxicity; and 5) alternative cell systems to primary human hepatocytes. We also report pharmaceutical perspectives of these topics and compare methods and interpretations for the drug development process.

Isolation, characterization, and differentiation to hepatocyte-like cells of nonparenchymal epithelial cells from adult human liver

Activation and proliferation of human liver progenitor cells has been observed during acute and chronic liver diseases. Our goal was to investigate the presence of these putative progenitors in the liver of patients who underwent lobectomy for various reasons but did not show any hepatic insufficiency. Hepatic lesions were evaluated by histological analysis. Nonparenchymal epithelial (NPE) cells were isolated from samples of human liver resections located at a distance from the lesion that motivated the operation and were cultured and characterized. These cells exhibited a marked proliferative potential. They did not express the classic set of stem cell/progenitor markers (Oct-4, Rex-1, alpha-fetoprotein, CD90, c-kit, and CD34) and were faintly positive for albumin. When cultured at confluence in the presence of hepatocyte growth factor and either epidermal growth factor or fibroblast growth factor-4, they entered a differentiation process toward hepatocytes. Their phenotype was quantitatively compared with that of mature human hepatocytes in primary culture. Differentiated NPE cells expressed albumin; alpha1-antitrypsin; fibrinogen; hepatobiliary markers such as cytokeratins 7, 19, and 8/18; liver-enriched transcription factors; and genes characterized by either a fetal (cytochrome P4503A7 and glutathione S-transferase pi) or a mature (tyrosine aminotransferase, tryptophan 2,3-dioxygenase, glutathione S-transferase alpha, and cytochrome P4503A4) expression pattern. NPE cells could be isolated from the liver of several patients, irrespective of the absence or presence of lesions, and differentiated toward hepatocyte-like cells with an intermediate hepatobiliary and mature/immature phenotype. These cells are likely to represent a resident progenitor population of the adult human liver, even in the absence of hepatic failure. Disclosure of potential conflicts of interest is found at the end of this article.

Differentiation of neonatal rat epithelial cells from biliary origin into immature hepatic cells by sequential exposure to hepatogenic cytokines and growth factors reflecting liver development

It was investigated whether cryopreserved rat liver epithelial cells (RLEC) from biliary origin are capable of undergoing hepatic differentiation upon sequential exposure to liver-specific factors (fibroblast growth factor (FGF)-4, hepatocyte growth factor (HGF), insulin-transferrin-sodium-selenite (ITS), dexamethasone (Dex) and oncostatin M (OSM)), reflecting liver embryogenesis in vivo. As differentiation progressed, cells acquired a hepatic morphology (polygonal-to-cuboidal shaped, binucleated cells), corresponding well with the phenotypic changes observed. Biliary cytokeratin (CK)19 and connexin (Cx)43-expression both gradually decreased; CK19-expression disappeared even completely. In contrast, hepatic CK18-expression persisted throughout the culture time. Hepatocyte nuclear factor (HNF)3beta, alpha-foetoprotein (AFP), transthyretin (TTR), HNF4, albumin (ALB), HNF1alpha, multidrug resistance protein (MRP)2 and Cx32 were expressed at specific stages during RLEC-differentiation, thereby showing a progressive hepatic maturation. Indeed, immature AFP and mature ALB were sequentially expressed, in line with the in vivo liver embryogenesis. Expression of the early and mid-late 'liver-enriched' transcription factors (LETF) HNF3beta and HNF4 declined and translocated to the cytosol, respectively, while the late LETF HNF1alpha underwent a nuclear upregulation. In conclusion, RLEC are bipotent cells, capable of differentiation into immature hepatocytes in a hepatic-stimulating micro-environment. The robustness of the sequential conditions, developed before for hepatic 'transdifferentiation' of rat bone marrow stem cells (rBMSC), was hereby confirmed.

The low-density lipoprotein receptor plays a role in the infection of primary human hepatocytes by hepatitis C virus

BACKGROUND/AIMS

The direct implication of low-density lipoprotein receptor (LDLR) in hepatitis C virus (HCV) infection of human hepatocyte has not been demonstrated. Normal primary human hepatocytes infected by serum HCV were used to document this point.

METHODS

Expression and activity of LDLR were assessed by RT-PCR and LDL entry, in the absence or presence of squalestatin or 25-hydroxycholesterol that up- or down-regulates LDLR expression, respectively. Infection was performed in the absence or presence of LDL, HDL, recombinant soluble LDLR peptides encompassing full-length (r-shLDLR4-292) or truncated (r-shLDLR4-166) LDL-binding domain, monoclonal antibodies against r-shLDLR4-292, squalestatin or 25-hydroxycholesterol. Intracellular amounts of replicative and genomic HCV RNA strands used as end point of infection were assessed by RT-PCR.

RESULTS

r-shLDLR4-292, antibodies against r-shLDLR4-292 and LDL inhibited viral RNA accumulation, irrespective of genotype, viral load or liver donor. Inhibition was greatest when r-shLDLR4-292 was present at the time of inoculation and gradually decreased as the delay between inoculation and r-shLDLR4-292 treatment increased. In hepatocytes pre-treated with squalestatin or 25-hydroxycholesterol before infection, viral RNA accumulation increased or decreased in parallel with LDLR mRNA expression and LDL entry.

CONCLUSIONS

LDLR is involved at an early stage in infection of normal human hepatocytes by serum-derived HCV virions.

A hepatitis C virus (HCV) NS3/4A protease-dependent strategy for the identification and purification of HCV-infected cells

As a tool for the identification and/or purification of hepatitis C virus (HCV)-infected cells, a chimeric form of the Gal4VP16 transcription factor was engineered to be activated only in the presence of the HCV NS3/4A protease and to induce different reporter genes [choramphenical acetyltransferase (CAT), green fluorescent protein (GFP) and the cell-surface marker H-2K(k)] through the (Gal4)(5)-E1b promoter. For this, the NS5A/5B trans-cleavage motif of HCV of genotype 1a was inserted between Gal4VP16 and the N terminus of the endoplasmic reticulum (ER)-resident protein PERK, and it was demonstrated that it could be cleaved specifically by NS3/4A. Accordingly, transient transfection in tetracycline-inducible UHCV-11 cells expressing the HCV polyprotein of genotype 1a revealed the migration of the Gal4VP16 moiety of the chimera from the ER to the nucleus upon HCV expression. Activation of the chimera provoked specific gene induction, as shown by CAT assay, first in UHCV-11 cells and then in Huh-7 cells expressing an HCV replicon of genotype 1b (Huh-7 Rep). In addition, the GFP reporter gene allowed rapid fluorescence monitoring of HCV expression in the Huh-7 Rep cells. Finally, the chimera was introduced into Huh-7.5 cells infected with cell culture-generated HCV JFH1 (genotype 2a), allowing the purification of the HCV-infected cells by immunomagnetic cell sorting using H-2K(k) as gene reporter. In conclusion, the Gal4VP16 chimera activation system can be used for the rapid identification and purification of HCV-infected cells.

Utility of long-term cultured human hepatocytes as an in vitro model for cytochrome p450 induction

Cytochrome P450 (P450) induction may have considerable implications for drug therapy. Therefore, understanding the induction potential of a new chemical entity at an early stage in discovery is crucial to reduce the risk of failure in the clinic and help the identification of noninducing chemical structures. Availability of human viable tissue often limits evaluation of induction potential in human hepatocytes. A solution is to increase the time period during which the hepatocytes remain viable. In this study we have investigated the induction of several P450 isozymes in long-term cultured hepatocytes compared with short-term cultured hepatocytes from the same individuals. Short- and long-term cultured primary hepatocytes isolated from each individual were cultured in a 96-well format and treated for 24 h with a range of prototypical P450 inducers and Merck Research Laboratories compounds. CYP3A4, 1A1, 1A2, 2B6, and 2C9 mRNA levels were measured using quantitative real-time reverse transcriptase-polymerase chain reaction (TaqMan) from the same cultured hepatocyte wells. CYP3A4, 1A1, 1A2, 2B6, and 2C9 were shown to be inducible in long-term cultured hepatocytes. The -fold induction varied between donors, and between short- and long-term cultured hepatocytes from the same donor. However, this variability can be controlled by normalizing data from each hepatocyte preparation to a positive control. The use of long-term cultured hepatocytes on 96-well plates has proven to be sensitive, robust, and convenient for assessing P450 induction potential of new compound entities during the drug discovery process.

In vitro protoscolicidal effects of hypertonic glucose on protoscolices of hydatid cyst

To evaluate the protoscolicidal effects of various concentrations of hypertonic glucose, live protoscolices of sheep were exposed to 10%, 15%, 25% and 50% glucose solutions. Cetrimide (0.5%), silver nitrate (0.5%) and hypertonic saline (20%) were used as positive controls, while physiological saline was used as a negative control. After 1, 2 and 5 min, the protoscolicidal effects were determined by 1% eosin. A 25% glucose solution had no significant protoscolicidal effect. However, a 50% glucose solution revealed higher protoscolicidal effect than 0.5% silver nitrate but weaker effect than 0.5% cetrimide; the effect was comparable with that of 20% hypertonic saline. The results showed that hypertonic glucose solution is highly effective in killing protoscolices of Echinococcus granulosus in vitro.

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.