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

Liposome-Mediated Gene Transfer in Differentiated HepaRG™ Cells: Expression of Liver Specific Functions and Application to the Cytochrome P450 2D6 Expression

The goal of this study was to establish a procedure for gene delivery mediated by cationic liposomes in quiescent differentiated HepaRG™ human hepatoma cells. We first identified several cationic lipids promoting efficient gene transfer with low toxicity in actively dividing HepG2, HuH7, BC2 and progenitor HepaRG™ human hepatoma cells. The lipophosphoramidate Syn1-based nanovector, which allowed the highest transfection efficiencies of progenitor HepaRG™ cells, was next used to transfect differentiated HepaRG™ cells. Lipofection of these cells using Syn1-based liposome was poorly efficient most likely because the differentiated HepaRG™ cells are highly quiescent. Thus, we engineered the differentiated HepaRG™ Mitogenic medium supplement (ADD1001) that triggered robust proliferation of differentiated cells. Importantly, we characterized the phenotypical changes occurring during proliferation of differentiated HepaRG™ cells and demonstrated that mitogenic stimulation induced a partial and transient decrease in the expression levels of some liver specific functions followed by a fast recovery of the full differentiation status upon removal of the mitogens. Taking advantage of the proliferation of HepaRG™ cells, we defined lipofection conditions using Syn1-based liposomes allowing transient expression of the cytochrome P450 2D6, a phase I enzyme poorly expressed in HepaRG cells, which opens new means for drug metabolism studies in HepaRG™ cells.

Transcriptomic characterization of bovine primary cultured hepatocytes; a cross-comparison with a bovine liver and the Madin-Darby bovine kidney cells

Bovine primary cultured hepatocytes (CHs) are widely used in vitro models for liver toxicity testing. However, little is known about their whole-transcriptome profile and its resemblance to the normal liver tissue. In the present study, we profiled - by microarray - the whole-transcriptome of bovine CHs (n=4) and compared it with the transcriptomic landscape of control liver samples (n=8), as well the Madin-Darby bovine kidney (MDBK) cells (n=4). Compared with liver tissue, the bovine CHs relatively expressed (fold change >2, P<0.05) about 2155 and 2073 transcripts at a lower and higher abundance, respectively. Of those expressed at a lower abundance, many were drug biotransformation enzyme-coding genes, such as the cytochrome P450 family (CYPs), sulfotransferases, methyltransferases, and glutathione S-transferases. Also, several drug transporters and solute carriers were expressed at a lower abundance in bovine CHs. 'Drug metabolism', 'PPAR signaling', and 'metabolism of xenobiotics by CYPs' were among the most negatively-enriched pathways in bovine CHs compared with liver. A qPCR cross-validation using 8 selected genes evidenced a high correlation (r=0.95, P=0.001) with the corresponding microarray results. Although from a kidney origin, and albeit to a lower extent compared to bovine CHs, the MDBK cells showed a basal expression of many CYP-coding genes. Our study provides a whole-transcriptome-based evidence for the bovine CHs and hepatic tissue resemblance. Overall, the bovine CHs' transcriptomic profile might render it unreliable as an in vitro model to study drug metabolism.

Efficient transfection of Xenobiotic Responsive Element-biosensor plasmid using diether lipid and phosphatidylcholine liposomes in differentiated HepaRG cells

In this study, we evaluated cationic liposomes prepared from diether-NH₂ and egg phosphatidylcholine (EPC) for in vitro gene delivery. The impact of the lipid composition, i.e. the EPC and Diether-NH₂ molar ratio, on in vitro transfection efficiency and cytotoxicity was investigated using the human HEK293T and hepatoma HepaRG cells known to be permissive and poorly permissive cells for liposome-mediated gene transfer, respectively. Here, we report that EPC/Diether-NH₂-based liposomes enabled a very efficient transfection with low cytotoxicity compared to commercial transfection reagents in both HEK293T and proliferating progenitor HepaRG cells. Taking advantage of these non-toxic EPC/Diether-NH₂-based liposomes, we developed a method to efficiently transfect differentiated hepatocyte-like HepaRG cells and a biosensor plasmid containing a Xenobiotic Responsive Element and a minimal promoter driving the transcription of the luciferase reporter gene. We demonstrated that the luciferase activity was induced by a canonical inducer of cytochrome P450 genes, the benzo[a]pyrene, and two environmental contaminants, the fluoranthene, a polycyclic aromatic hydrocarbon, and the endosulfan, an organochlorine insecticide, known to induce toxicity and genotoxicity in differentiated HepaRG cells. In conclusion, we established a new efficient lipofection-mediated gene transfer in hepatocyte-like HepaRG cells opening new perspectives in drug evaluation relying on xenobiotic inducible biosensor plasmids.

A hybrid substratum for primary hepatocyte culture that enhances hepatic functionality with low serum dependency

Cell culture systems have proven to be crucial for the in vitro maintenance of primary hepatocytes and the preservation of hepatic functional expression at a high level. A poly-(N-p-vinylbenzyl-4-O-β-D-galactopyranosyl-D-gluconamide) matrix can recognize cells and promote liver function in a spheroid structure because of a specific galactose–asialoglycoprotein receptor interaction. Meanwhile, a fusion protein, E-cadherin-Fc, when incubated with various cells, has shown an enhancing effect on cellular viability and metabolism. Therefore, a hybrid substratum was developed for biomedical applications by using both of these materials to combine their advantages for primary hepatocyte cultures. The isolated cells showed a monolayer aggregate morphology on the coimmobilized surface and displayed higher functional expression than cells on traditional matrices. Furthermore, the hybrid system, in which the highest levels of cell adhesion and hepatocellular metabolism were achieved with the addition of 1% fetal bovine serum, showed a lower serum dependency than the collagen/gelatin-coated surface. Accordingly, this substrate may attenuate the negative effects of serum and further contribute to establishing a defined culture system for primary hepatocytes.

Transfection of Primary Hepatocytes with Liver-Enriched Transcription Factors Using Adenoviral Vectors

Primary cultured hepatocytes are probably the best model to study endogenous metabolic pathways, toxicity, or drug metabolism. Many of these studies require expression of ectopic genes. It would be desirable to use a method of transfection that allows dose-response studies, high efficiency of transfection, and the possibility to express several genes at the same time. Adenoviral vectors fulfill these requirements, becoming a valuable tool for primary hepatocyte transfection. Moreover, they are easy to generate and do not require a high level of biocontainment. In the present chapter, we describe the generation, cloning, amplification, and purification of an adenoviral vector capable of infecting primary cultured hepatocytes. This recombinant adenovirus induces robust expression of the protein of interest in hepatocytes within a wide range of doses.

Can hepatoma cell lines be redifferentiated to be used in drug metabolism studies?

Knowledge of metabolism, enzymes so far involved, and potential enzyme-inhibiting or enzyme-inducing properties of new compounds is a key issue in drug development. Primary cultured hepatocytes, cytochrome P450 (CYP)-engineered cells and hepatoma cell lines are currently being used for this purpose, but only primary cultures can produce a metabolic profile of a drug similar to that found in vivo and can respond to inducers. Because of their limited accessibility, alternatives to replace human hepatocytes are currently being explored, including the immortalisation of hepatocytes by using different strategies (i.e. SV40 T-large antigen, conditionally immortalised hepatocytes, transfection with c-myc, cH-ras, N-ras oncogenes, transgenic animals over-expressing growth factors or oncogenes and cre-lox recombination/excision). However, none of the resulting cells has the desirable phenotypic characteristics to replace primary cultures in drug metabolisms studies. We investigated why these differentiated human hepatomas do not express CYP genes and found that the levels of certain key transcription factors clearly differ from those found in hepatocytes. It was then conceivable that re-expression of one (or more) of these transcription factors could lead to an efficient transcription of CYP genes. The feasibility of this hypothesis was demonstrated by genetic engineering of Hep G2 cells with liver-enriched transcription factors followed by the analysis of the expression of the most relevant human CYPs.

Efficient gene delivery by EGF-lipoplexes in vitro and in vivo

Aims: In this work, we have evaluated the ability of targeted lipoplexes to enhance transgene expression in EGF receptor (EGFR) overexpressing tumor cells by using lipoplexes. Materials & methods: We prepared DOTAP/cholesterol liposomes modified with EGF at 0.5/1, 1/1, 2/1 and 5/1 lipid/DNA (+/-) charge ratio by sequentially mixing the liposomes with the ligand and adding the reporter or the therapeutic plasmid gene, pCMVLuc (pVR1216) or pCMVIL12, respectively. HepG2, DHDK12proB and SW620 cells were used for in vitro experiments, which were performed in the presence of 60% serum. Results: The characterization of EGF-lipoplexes indicated a size close to 300 nm and a variable net surface charge as a function of the amount of EGF associated to the cationic liposomes. EGF-lipoplexes, which showed an increased transfection activity, were positively charged, noncytotoxic and highly effective in protecting DNA from DNase I attack. Transfection activity in vitro resulted in an enhancement in the luciferase and IL-12 expression by EGF-lipoplexes compared with those without ligand (plain-lipoplexes) and to naked DNA. The results observed in SW620 cells, which are deficient in EGFR, confirmed that DNA uptake was predominantly via EGFR-mediated endocytosis. In vivo transfection activity was confirmed by luciferase imaging in living mice. Bioluminiscence could be detected mainly in the lung with a maximum signal 24 h after application. The resulting EGF-lipoplexes significantly increased the level of gene expression in mice compared with control or naked DNA. Conclusion: These findings indicate that these nanovectors may be an adequate alternative to viral vectors for gene therapy.

[Adipose tissue-derived stem cells: hepatic plasticity]

Currently, the only effective treatment for end-stage liver disease is liver transplantation. The number of patients on the waiting list increases considerably each year, giving rise to a wide imbalance between supply and demand for healthy livers. Knowledge of stem cells and their possible use have awakened great interest in the field of hepatology, these cells being one of the most promising short-term alternatives. Hepatic stem cell therapy consists of the implantation of healthy cells capable of performing the functions that damaged cells are unable to carry out. Recent observations indicate that several stem cells can differentiate into distinct cell lineages. Hepatic differentiation of adult stem cells from several origins has yielded highly promising results. Adipose tissue in adults contains a reservoir of stem cells that can be induced and differentiated into different types of cells, showing a high degree of plasticity. Because of its abundance and easy access, adipose tissue is a promising source of adult stem cells for hepatic stem cell therapy. The present article reviews the progress made in the differentiation of adult stem cells from adipose tissue into cells with hepatic phenotype. We also discuss the potential application of this technique as a therapy for temporary metabolic support in patients with end-stage liver failure awaiting whole organ transplantation, as a method to support liver function and facilitate regeneration of the native liver in cases of fulminant hepatic failure, and as a treatment in patients with genetic metabolic defects in vital liver functions.

Hepatocyte cell lines: their use, scope and limitations in drug metabolism studies

Gaining knowledge on the metabolism of a drug, the enzymes involved and its inhibition or induction potential is a necessary step in pharmaceutical development of new compounds. Primary human hepatocytes are considered a cellular model of reference, as they express the majority of drug-metabolising enzymes, respond to enzyme inducers and are capable of generating in vitro a metabolic profile similar to what is found in vivo. However, hepatocytes show phenotypic instability and have a restricted accessibility. Different alternatives have been explored in the past recent years to overcome the limitations of primary hepatocytes. These include immortalisation of adult or fetal human hepatic cells by means of transforming tumour virus genes, oncogenes, conditionally immortalised hepatocytes, and cell fusion. New strategies are currently being used to upregulate the expression of drug-metabolising enzymes in cell lines or to derive hepatocytes from progenitor cells. This paper reviews the features of liver-derived cell lines, their suitability for drug metabolism studies as well as the state-of-the-art of the strategies pursued in order to generate metabolically competent hepatic cell lines.

Fuentes alternativas de hepatocitos para la terapia celular

There is an urgent need to search for alternatives to whole organ transplantation. Several methods have been proposed. Among these strategies, cell transplantation is currently one of the most promising. To achieve this aim, in addition to highly differentiated adult hepatocytes, the use of stem cells is considered a highly attractive therapeutic method for the treatment of liver disease and for temporary support of hepatic function until a liver becomes available for organ transplantation. This strategy is based on the ability of stem cells to differentiate into different cellular types according to their environment. Therefore, stem cells could be an unlimited source of hepatic cells for transplantation and gene therapy. Bone marrow is considered the most promising source of adult stem cells, partly due to the versatility of the cells obtained in repairing damaged tissues of several lineages. Several different types of stem cells have been described in bone marrow: hematopoietic, mesenchymal, side population and multipotent adult stem cells. Bone marrow cells have been hypothesized as a third recruitment source in liver regeneration in addition to hepatocytes and endogenous liver stem cells. Consequently, attempts have been made to differentiate them into hepatic lineage for their subsequent use in hepatic cell therapy. The present article reviews the progress made in this field or research.

Interferon-alpha stimulation of liver cells enhances hepatitis delta virus RNA editing in early infection

BACKGROUND/AIMS

RNA editing controls the formation of hepatitis-delta-antigen-S and -L and therefore plays a central role in the hepatitis-delta-virus (HDV) life-cycle. Editing is catalyzed by the enzyme Adenosine-deaminase-acting-on-RNA1 (ADAR1) of which two different forms, ADAR1-L and ADAR1-S, exist. As ADAR1-L is induced by interferon (IFN)-alpha, we examined the influence of IFN-alpha-stimulation of host cells on HDV-RNA editing.

METHODS

Editing was studied in Huh-7-cells transfected with HDV-RNA on days 7, 14, 21 and 28 after transfection. ADAR1-L mRNA was measured by RT-PCR.

RESULTS

IFN-alpha-treatment led to a 5-fold higher expression of ADAR1-L and to an increase in editing from 14+/-2% (SD) in unstimulated controls to 27+/-4% (SD) on day 7 after transfection. Editing further increases over time to the same maximum level of 35% in IFN-alpha-treated as well as untreated cells.

CONCLUSIONS

By IFN-alpha-stimulation both ADAR1-L expression and editing are increased in Huh-7-cells at day 7, and the maximum level of edited antigenomes is reached earlier with IFN-alpha-treatment as compared to untreated cells. Thus, ADAR1-L appears to be able to increase editing, but the HDV genome apparently has an intrinsic negative feed-back regulation mechanism that limits editing to roughly a third of the genomes.

Transfection efficiency and cytotoxicity of cationic liposomes in salmonid cell lines of hepatocyte and macrophage origin

The transfection efficiency of liposome-based DNA formulations was studied in different salmonid cell lines of hepatocyte and macrophage origin. Parallel assessment of cell viability was carried out to define the balance between transfection efficiency and toxicity. For all cell lines, transfection efficiency varied with the lipoplex charge ratio and the amount of DNA added to the liposomes. The hepatocyte-derived cell line was most readily transfected while lower transfection efficiency was observed for the macrophage cell lines. The cationic liposomes showed a dose-dependent toxicity and were found to be most toxic for cells of macrophage origin. This was in line with the observation that higher amounts of lipids were associated with the cells of macrophage origin than the hepatocytes. Complexing DNA with the liposomes reduced the toxicity for all three cell lines, most markedly, however, for macrophage cell lines. The differences in the transfection and toxicity patterns between the cell lines are probably caused by differences in membrane composition as well as differences in phagocytic activity and processing of the liposomes/lipoplexes.

Analysis of differential lipofection efficiency in primary and established myoblasts

In this study we have compared the process of lipid-mediated transfection in primary and established myoblasts, in an attempt to elucidate the mechanisms responsible for the scarce transfectability of the former. We determined the metabolic stability of cytoplasmically injected and lipofected DNA in primary and established myoblasts and carried out a comparative time course analysis of luciferase reporter-gene expression and DNA stability. The efficiency of the transcription-translation machinery of the two cell types was compared by intranuclear injection of naked plasmid DNA encoding luciferase. Subcellular colocalization of fluorescein-labeled lipopolyplexes with specific endosomal and lysosomal markers was performed by confocal microscopy to monitor the intracellular trafficking of plasmid DNA during transfection. The metabolic stability of plasmid DNA was similar in primary and established myoblasts after both lipofection and cytoplasmic injection. In both cell types, lipofection had no detectable effect on the rate of cell proliferation. Confocal analysis showed that nuclear translocation of transfected DNA coincided with localization in a compartment devoid of endosome- or lysosome-specific marker proteins. The residency time of plasmid DNA in this compartment differed for primary and established myoblasts. Our findings suggest that the lower transfectability of primary myoblasts is mostly due to a difference in the intracellular delivery pathway that correlates with more rapid delivery of internalized complex to the lysosomal compartment.

Baculovirus vectors repress phenobarbital-mediated gene induction and stimulate cytokine expression in primary cultures of rat hepatocytes

Baculovirus transfection strategies have proven successful at transferring foreign DNA into hepatoma cells and primary hepatocytes. When testing the utility of these methodologies in cultured hepatocytes, we discovered that the presence of baculovirus disrupts the phenobarbital (PB) gene induction process, a potent transcriptional activation event characteristic of highly differentiated hepatocytes, and repressed expression of the albumin gene. In concert with previous reports from our laboratory demonstrating that increased cAMP levels can completely repress the induction of specific cytochrome P450 (CYP) genes, cAMP concentrations and PKA activities were measured in the primary hepatocytes subsequent to baculovirus exposure. However, neither parameter was affected by the presence of the virus. To evaluate whether immune response modulation was triggered by baculovirus exposure, RNase protection assays were performed and demonstrated that baculovirus infection activates TNF-alpha, IL-1alpha and IL-1beta expression in the primary hepatocyte cultures. Immunocytochemical experiments indicated that the production of cytokines was likely due to the presence of small numbers of Kupffer cells present in the culture populations. Exogenously added TNF-alpha was also effective in repressing PB induction, consistent with other reports indicating that inflammatory cytokines are capable of suppressing expression of biotransformation enzyme systems. Comparative studies demonstrated the specificity of these effects since exposures of hepatocytes to adenoviral vectors did not result in down-regulation of hepatic gene responsiveness. These results indicate that baculovirus vectors enhance the expression of inflammatory cytokines in primary hepatocyte cultures, raising concerns as to whether these properties will compromise the use of baculovirus vectors for study of cytochrome P450 gene regulation, as well as for liver-directed gene therapy in humans.

Nuclear-associated plasmid, but not cell-associated plasmid, is correlated with transgene expression in cultured mammalian cells

Intracellular plasmid is rapidly incorporated into the nucleus of HeLa cells following cationic lipoplex transfection. CV1 cells are less effective in translocating plasmid to the nucleus and also express less transgene than HeLa cells. Cultured HeLa and CV1 cells and corresponding isolated nuclei were analyzed after transfection of a Cy3-labeled pGreenLantern plasmid (Cy3-pGL). Flow cytometry was used to measure both plasmid delivery and transgene expression from the plasmid encoding a CMV promoter-driven green fluorescent protein. During transfection, HeLa cells rapidly incorporated the plasmid, reaching a maximum of 80% Cy3-pGL positive cells 8 h posttransfection. The average Cy3-pGL-positive HeLa cell contained approximately 2470 plasmid copies. Forty-eight percent of the nuclei isolated from the transfected HeLa cells were positive for the plasmid marker after 8 h. In contrast to HeLa cells, fewer CV1 cells and CV1 nuclei incorporated plasmid DNA with peak transfection occurring after 12 h for 36% of the cells and after 8 h for 12% of the nuclei. However, the average Cy3-pGL-positive CV1 cell did not have a significantly different number of total cellular plasmid copies than the average positive HeLa cell. CV1 nuclei, however, had half as much nuclear associated plasmid as HeLa nuclei. HeLa cells are more efficient than CV1 cells at transporting plasmid from the cytoplasm to the nucleus. This study demonstrates the use of a novel quantitative method to study plasmid transport from the cytoplasm to the nucleus and the effect on transgene expression.

Phenobarbital responsiveness conferred by the 5'-flanking region of the rat CYP2B2 gene in transgenic mice

Phenobarbital (PB) is a prototype for a class of agents that produce marked transcriptional activation of a number of genes, including certain cytochrome P-450s. We used transgenic mouse approaches and multiple gene reporters to assess the functional consequences of specific deletions and site-specific mutations within the 2.5kb 5'-flanking region of the rat CYP2B2 gene. Protein-DNA interactions at the PBRU domain also were characterized. Using the transgenic models, we demonstrate that sequences between -2500 and -1700bp of the CYP2B2 gene are critical for PB induction; mice with 1700 or 800bp of 5'-flanking CYP2B2 sequence are not PB responsive. DNA affinity enrichment techniques and immunoblotting and electromobility shift assays were used to determine that nuclear factor 1 (NF-1) interacts strongly with a site centered at -2200bp in the PB responsive unit (PBRU) of CYP2B2. To test the functional contribution of NF-1 in PB activation, we introduced specific mutations within the PBRU NF-1 element and demonstrated that these mutations completely ablate the binding interaction. However, transgenic mice incorporating the mutant NF-1 sequence within an otherwise wild-type -2500/CYP2B2 transgene maintained full PB responsiveness. These results indicate that, despite the avidity of the respective DNA-protein interaction within the PBRU in vitro, NF-1 interaction is not an essential factor directing PB transcriptional activation in vivo.

Hepatitis B virus replication in human HepG2 cells mediated by hepatitis B virus recombinant baculovirus

A novel transient mechanism for studying hepatitis B virus (HBV) gene expression and replication using recombinant HBV baculovirus to deliver the HBV genome to HepG2 cells was generated. In HBV baculovirus infected HepG2 cells, HBV transcripts, and intracellular and secreted HBV antigens are produced; replication occurs as evidenced by the presence of high levels of intracellular replicative intermediates and protected HBV DNA in the medium. Density-gradient analysis of extracellular HBV DNA indicated that the DNA was contained predominantly in enveloped HBV virions. Covalently closed circular (CCC) DNA is present indicating that, in this system, HBV core particles are capable of delivering newly synthesized HBV genomes back into the nuclei of infected cells. HBV gene expression is driven exclusively from endogenous promoters. Levels of HBV gene expression and replication can be achieved in HBV baculovirus-infected HepG2 cells which far exceed levels found in HepG2 2.2.15 cells. HBV baculovirus infection of HepG2 cells lends itself readily to experimental manipulation as follows: 1) HBV expression can be initiated any time relative to seeding of HepG2 cells; 2) levels of HBV replication can be regulated over a wide range simply by changing the baculovirus multiplicity of infection; 3) HBV replication is readily detectable by one day post infection with HBV baculovirus and persists at least through day eleven post infection; and (4) the transient nature of the infection can be extended and/or enhanced by superinfecting the cultures. We conclude that infection of HepG2 cells by HBV recombinant baculovirus represents a simple to use and highly flexible system for studying the effects of antivirals and/or cytokines on HBV production and for understanding HBV replication and pathogenesis at the molecular level.

The antibiotic rifampicin is a nonsteroidal ligand and activator of the human glucocorticoid receptor

The glucocorticoid receptor (GR) belongs to a superfamily of ligand-regulated nuclear steroid hormone receptors. The steps in the signal transduction pathway leading to the biological effects of glucocorticoids (GCs) include sequentially binding of the steroid to the GR ligand binding domain (LBD), receptor transformation, nuclear translocation and either positive or negative gene transactivation. Rifampicin (RIF) is a macrocyclic antibiotic used as an antituberculosis agents. As the incidence of tuberculosis has been increasing, in part because of the AIDS epidemic, a growing number of patients are being exposed to the adverse effects of this antibiotic. Indeed, this compound, as are the GCs, is often implicated in noxious drug interactions, because of its strong ability to induce drug-metabolizing enzymes. Moreover, in humans, RIF, as are the GCs, has been described as a potential immunodepressor, associated notably with the reduction of mitogenic responsiveness of human peripheral blood lymphocytes. Here, we report that RIF activates the human glucocorticoid receptor (hGR). Transient expression of wild-type, deleted or mutated GRs; sucrose density gradient sedimentation; and the BIAcore technique strongly suggest that RIF binds to the receptor with the physiological consequence that this antibiotic acts as an immunodepressor. Given the wide use of RIF in the treatment of coinfection of tuberculosis and HIV, this report is highly relevant to current medical practice.