Primary cultures of human hepatocytes: a unique system for studies in toxicology, virology, parasitology and liver pathophysiology in man

The human hepatocyte cell lines IHH and HepaRG: models to study glucose, lipid and lipoprotein metabolism

Metabolic diseases reach epidemic proportions. A better knowledge of the associated alterations in the metabolic pathways in the liver is necessary. These studies need in vitro human cell models. Several human hepatoma models are used, but the response of many metabolic pathways to physiological stimuli is often lost. Here, we characterize two human hepatocyte cell lines, IHH and HepaRG, by analysing the expression and regulation of genes involved in glucose and lipid metabolism. Our results show that the glycolysis pathway is activated by glucose and insulin in both lines. Gluconeogenesis gene expression is induced by forskolin in IHH cells and inhibited by insulin in both cell lines. The lipogenic pathway is regulated by insulin in IHH cells. Finally, both cell lines secrete apolipoprotein B-containing lipoproteins, an effect promoted by increasing glucose concentrations. These two human cell lines are thus interesting models to study the regulation of glucose and lipid metabolism.

Distinct regulation of adiponutrin/PNPLA3 gene expression by the transcription factors ChREBP and SREBP1c in mouse and human hepatocytes

BACKGROUND & AIMS

The adiponutrin/PNPLA3 (patatin-like phospholipase domain-containing protein 3) variant I148M has recently emerged as an important marker of human fatty liver disease. In order to understand the role of the adiponutrin/PNPLA3 protein, we investigated the regulation of its expression in both human and mouse hepatocytes.

METHODS

Adiponutrin/PNPLA3 and lipogenic enzyme expression was determined by real-time PCR analysis in a wide panel of analysis in vivo in the mouse liver and in vitro in murine hepatocytes and human hepatocyte cell lines infected with ChREBP or SREBP1c-expressing adenoviruses.

RESULTS

We show that in the mouse liver, adiponutrin/PNPLA3 gene expression is under the direct transcriptional control of ChREBP (carbohydrate-response element-binding protein) and SREBP1c (sterol regulatory element binding protein1c) in response to glucose and insulin, respectively. In silico analysis revealed the presence of a ChoRE (carbohydrate response element) and of a SRE (sterol response element) binding site on the mouse adiponutrin/PNPLA3 gene promoter. Point mutation analysis in reporter gene assays identified the functional response of these two binding sites in the mouse adiponutrin/PNPLA3 promoter. In contrast, in human immortalized hepatocytes and in HepG2 hepatoma cells, only SREBP1c was able to induce adiponutrin/PNPLA3 expression, whereas ChREBP was unable to modulate its expression.

CONCLUSIONS

All together, our results suggest that adiponutrin/PNPLA3 is regulated by two key factors of the glycolytic and lipogenic pathways, raising the question of its implication in the metabolism of carbohydrates and lipids.

Plasticity of hepatic cell differentiation: bipotential adult mouse liver clonal cell lines competent to differentiate in vitro and in vivo

In fetal liver, bipotential hepatoblasts differentiate into hepatocytes and bile duct cells (cholangiocytes). The persistence of such progenitor cells in adult mouse liver is still debated. In damaged liver of adult murine animals, when hepatocyte proliferation is compromised, bipotential oval cells emerge, probably from bile ducts, proliferate, and differentiate to regenerate the liver. However, treatment to elicit oval cell proliferation is not necessary to obtain bipotential stem cells from adult mouse liver. Here, we have isolated bipotential clonal cell lines from healthy liver of 8-10-week-old C57BL/6 mice. Primary cultures established from hepatocyte-enriched suspensions were characterized by time-lapse image acquisition, immunocytology, and RNA transcript analysis. Although hepatocytes dedifferentiated with loss of apical polarity and other hepatocyte markers, they rapidly activated expression of bile duct/oval cell markers. Reversibility of these processes was achieved in part by culture under dilute Matrigel or by aging of confluent cultures. Cell lines were obtained at high frequency from mass cultures, from isolated colonies, and by primary cloning of the hepatocyte-enriched suspension. Cells of the clonal cell lines do not grow in soft agar and are nontumorigenic, and they express cytokeratin 19, A6 antigen, and alpha6 integrin, as well as a large panel of hepatocyte functions. Furthermore, they can participate in liver regeneration in albumin-urokinase-type plasminogen activator/severe combined immune-deficient mice, where they differentiate in clusters of hepatocytes and occasionally bile ducts. These results demonstrate the existence, in normal adult mouse liver, of a significant pool of clonogenic cells that are (or can become) bipotential.

Induction of cytochrome P450 (CYP)1A1, CYP1A2, and CYP3A4 but not of CYP2C9, CYP2C19, multidrug resistance (MDR-1) and multidrug resistance associated protein (MRP-1) by prototypical inducers in human hepatocytes

Human hepatocytes cultured serum-free for up to 6 weeks were used to study expression and induction of enzymes and membrane transport proteins involved in drug metabolism. Phase I drug metabolizing enzymes cytochrome P450 (CYP)1A1, CYP1A2, CYP2C9, CYP2C19, CYP2E1, and CYP3A4 were detected by Western blot analyses and, when appropriate, by enzymatic assays for ethoxyresorufin-O-deethylase(EROD)-activity and testosterone-6beta-hydroxylase(T6H)-activity. Expression of the membrane transporter multi-drug resistance protein (P-glycoprotein, MDR-1), multidrug resistance-associated protein (MRP-1), and lung-resistance protein (LRP) was maintained during the culture as detected by RT-PCR and Western blot analyses. Model inducers like rifampicin, phenobarbital, or 3-methylcholanthrene and beta-naphtoflavone were able to induce CYP1A or CYP3A4 as well as EROD or T6H activities for up to 30 days. CYP2C9, CYP2C19 and CYP2E1 expression was maintained but not inducible for 48 days. Also, rifampicin and phenobarbital were unable to increase MDR-1 and MRP-1 protein levels significantly.

Serum-free, long-term cultures of human hepatocytes: maintenance of cell morphology, transcription factors, and liver-specific functions

Since human hepatocytes are available only in limited number, the development of a serum-free culture system for long-term cultivation of differentiated and functional hepatocytes is of great importance. Here we describe the culture of human hepatocytes in a chemically defined serum-free medium for up to 5 weeks. Cell morphology was assayed by light and electron microscopy and revealed a well-preserved cellular morphology. Marker proteins for epithelial and bile duct cells, cytokeratin (CK) 18 and 19, and liver-specific proteins, like phosphoenolpyruvate carboxykinase-2 (PCK2) and serum proteins, were expressed. Liver-enriched transcription factors CCAAT/enhancer binding protein alpha (C/EBPalpha) and hepatocyte nuclear factor-4 (HNF-4), cytokine and mitogen activated factors (nuclear factor kappa B) NFkappaB, and activator protein-1 (AP-1) were maintained and active for several weeks in our cultures. In summary, our serum-free culture system allows the culture of differentiated human hepatocytes for several weeks. It may serve as a model system for metabolic, pharmacologic-toxicologic studies, and studies on human pathogens under defined chemical conditions.

Identification and characterization of receptor for mammalian hepatopoietin that is homologous to yeast ERV1

Hepatopoietin (HPO) is a novel polypeptide mitogen specific for hepatocytes and hepatoma cell lines, which is derived from liver and supports its regeneration. To determine whether HPO acts via a receptor-based signal transduction, recombinant human hepatopoietin was labeled by iodination and used to characterize its binding activity by specific displacement test and Scatchard analysis in primarily cultured rat hepatocytes and human hepatoma Hep-G2 cells. The binding was saturable and specific because it was replaceable by HPO but not by epidermal growth factor, transforming growth factor-alpha, or insulin. Scatchard analysis indicated the presence of a single class of high affinity receptor with dissociation constant (Kd) of 2 and 0.7 pM, and a receptor density of about 10, 000 sites/cell and 55,000 sites/cell in the rat hepatocytes and human hepatoma cells, respectively. The Kd values were consistent with the half-maximum dose of HPO activity. Affinity cross-linking of the receptor with 125I-HPO revealed a polypeptide of molecular mass approximately 90 kDa by SDS-polyacrylamide gel electrophoresis. Thus, the molecular mass of the HPO receptor was calculated to be about 75 kDa. These data demonstrated the existence of an HPO receptor in hepatocytes and hepatoma cells, which may account for biological effect.

Simplified isolation and spheroidal aggregate culture of rat hepatocytes

AIM: To explore a simplified method for isolation of hepatocytes and establish a method of primary hepatocyte culture with more aggregates and longer persisence.

METHODS: Wistar rat hepatocytes were isolated by a single extracorporeal two-step perfusion method, and the cells were seeded on poly-HEMA coated flasks and cultured with hormonally defined medium and gentle shaking at regular intervals.

RESULTS: The total yield of isolating hepatocytes amounted to 10⁸ cells for each rat liver with the viability of more than 90% in all isolations. Under the nonadherent environments, the cells were found to attach to each other and form multicellular aggregates rapidly, and the aggregates became spheroidal shape after two days in culture. The morphologic characteristics and albumin synthetic function of the multicellular spheroidal aggregates can be maintained for one month.

CONCLUSION: The simple and reliable isolation as well as large scale and longer time culture of hepatocytes can be used for experiments in liver cell transplantation and bioartificial liver support system.

Prediction of in vivo drug interaction from in vitro systems exemplified by interaction between verapamil and cimetidine using human liver microsomes and primary hepatocytes

Emphasis on drug safety is increasing as newly developed drugs become more potent. Interest in the prediction and description of drug interactions is growing accordingly. The study of potential interactions at a very early stage of drug development requires suitable in vitro models that describe drug interactions both qualitatively and quantitatively. The purpose of the work described here was to help assess the predictive value of in vitro drug interaction tests with liver microsomes and hepatocytes by means of the interaction between verapamil and cimetidine. The in vitro inhibition of verapamil metabolism by cimetidine observed during the studies was quantitatively similar to the results reported in published clinical studies after intravenous application. Studies using liver microsome fractions showed that the intrinsic clearances for the formation of various metabolites could be used to predict drug interactions. In addition, work with hepatocyte cultures revealed that an in vitro system covering both phase I and phase II reactions should be included in such studies to permit quantitative prediction of the various metabolic pathways. Both human hepatocyte cultures and human microsomes offer certain advantages for predicting the degree of drug metabolism and interactions in humans at the biotransformation level. Therefore, it seems likely that the simultaneous application of both systems will yield conclusions that most closely approximate the situation in humans.

Functional activity of isolated pig hepatocytes attached to different extracellular matrix substrates. Implication for application of pig hepatocytes in a bioartificial liver

For the manufacture of a bioartificial liver for human application, large amounts of viable and active hepatocytes are needed. Pig hepatocytes are considered to be the best alternative to scarce human hepatocytes. In vitro hepatocyte functions have so far been tested under different circumstances, mainly with rat hepatocytes. Pig hepatocytes were isolated with a single two-step isolation procedure, resulting in a high yield of viable hepatocytes. The hepatocytes were tested for their ability to synthesise urea, to metabolise 7-ethoxycoumarin (cytochrome P450 activity), and to synthesise and secrete proteins. These activities of hepatocytes while attached to tissue culture plastic were compared to the activity of the cells attached to several extracellular matrix constituents: collagen I and IV, laminin, fibronectin, Engelbreth-Holm-Swarm Natrix and in the presence of Matrigel. With the exception of Matrigel, neither of the extracellular matrix substrates enhanced pig hepatocyte function compared to tissue culture plastic. However, relatively large amounts of murine proteins leak out of the Matrigel. The advisability of using Matrigel or other extracellular matrix proteins in a bioartificial liver loaded with pig hepatocytes is discussed.

Differential effects of eicosapentaenoic acid on glycerolipid and apolipoprotein B metabolism in primary human hepatocytes compared to HepG2 cells and primary rat hepatocytes

We compared the effects of eicosapentaenoic acid (EPA) and oleic acid (OA) on glycerolipid and apolipoprotein B (apoB) metabolism in primary human hepatocytes, HepG2 cells and primary rat hepatocytes. Cells were incubated for 1 to 5 h with 0.25 mM bovine serum albumin in the absence (control) or presence of 1 mM of EPA or OA. Synthesis and secretion of [3H]glycerolipid were determined after 1 h incubation with [3H]glycerol. Cellular and medium apoB abundance was semi-quantitatively estimated in human cells by Western blotting. The following observations were made. (1) Compared to control, OA induced a 7-fold increase in [3H]triacylglycerol (TG) synthesis in human hepatocytes and a 4-fold increase in rat hepatocytes and HepG2 cells. EPA enhanced [3H]TG synthesis about 2-fold in all three cell types although it stimulated [3H]diacylglycerol (DG) synthesis to an extent (i.e., 2.5- to 5-fold) similar to OA. (2) In contrast to OA, which stimulated VLDL-associated [3H]TG secretion 2.5- to 3-fold in the three cell types relative to control, EPA did not alter [3H]TG secretion in HepG2 and rat hepatocytes and suppressed [3H]TG secretion by 75% in primary human hepatocytes. (3) In primary human hepatocytes, both OA and EPA did not alter cellular apoB abundance but EPA decreased apoB secretion by 44% as compared to control. In contrast, both EPA and OA increased cellular and medium apoB abundance 2- to 2.5-fold in HepG2 cells, although medium apoB tended to be lower in EPA-treated cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative metabolism of SC-42867 and SC-51089, two PGE2 antagonists, in rat and human hepatocyte cultures

1. The metabolism of SC-42867 and SC-51089, two PGE2 antagonists, was studied in cultured rat and human hepatocytes. Both compounds possess an 8-chlorodibenzoxazepine moiety, but differ from each other by the nature of the side chain connected to the nitrogen atom. SC-42867 and SC-51089 and their in vitro metabolites were separated by reversed-phase hplc. The major metabolites of both compounds were identified by mass spectrometry (ms) analysis. 2. SC-42867 was metabolized on the tricyclic moiety only. Oxidative N-dealkylation with opening of the oxazepine ring was the major metabolic pathway obtained in rat hepatocytes. The metabolic profile obtained in cultured human hepatocytes was comparable with that of cultured rat hepatocytes. However, the compound was metabolized to a much lower extent by the human cells. 3. SC-51089 was extensively metabolized by both cultured rat and human hepatocytes. Human cells metabolized this compound quite differently than cultured rat hepatocytes. Aromatic hydroxylation with consequent glucuronidation and sulphation were the main metabolic pathways observed in cultured human hepatocytes. Oxidative N-dealkylation with opening of the oxazepine ring and consequent glucuronidation was the major metabolic pathway observed in rat hepatocytes. Further metabolism occurred, in contrast with the human hepatocytes, mainly on the side chain. 4. The present in vitro results are compared with data of previous in vivo studies performed in rat.

Susceptibility of human liver cell cultures to hepatitis C virus infection

To develop a cell culture system susceptible to infection by hepatitis C virus (HCV), human fetal hepatocytes, grown in serum-free medium, were inoculated with serum samples from two HCV-infected patients. Viral RNA sequences were detected by polymerase chain reaction, using primers specific for the 5' noncoding region of HCV, in extracts prepared from the hepatocyte cultures as early as 5 days after inoculation. Virus was also released from the infected cells into the medium. The HCV strains could be serially passaged three times into fresh liver cell cultures using intracellular virus as inoculum. Evidence that HCV replication really took place in primary human fetal hepatocytes was also obtained by detection of minus-strand viral RNA (replication intermediate) in cell extracts and of viral antigens in the infected cells.