Cellular models for the screening and development of anti-hepatitis C virus agents. Pharmacol Ther. 2009;124:1-22. [PMID: 19555718 DOI: 10.1016/j.pharmthera.2009.05.010]

Hepatitis C virus: Morphogenesis, infection and therapy

Hepatitis C virus (HCV) is a major cause of liver diseases including liver cirrhosis and hepatocellular carcinoma. Approximately 3% of the world population is infected with HCV. Thus, HCV infection is considered a public healthy challenge. It is worth mentioning, that the HCV prevalence is dependent on the countries with infection rates around 20% in high endemic countries. The review summarizes recent data on HCV molecular biology, the physiopathology of infection (immune-mediated liver damage, liver fibrosis and lipid metabolism), virus diagnostic and treatment. In addition, currently available in vitro, ex vivo and animal models to study the virus life cycle, virus pathogenesis and therapy are described. Understanding of both host and viral factors may in the future lead to creation of new approaches in generation of an efficient therapeutic vaccine.

Hepatitis C virus infection: Are there still specific problems with genotype 3?

Hepatitis C virus (HCV) infection is one of the most common causes of chronic liver disease and the main indication for liver transplantation worldwide. As promising specific treatments have been introduced for genotype 1, clinicians and researchers are now focusing on patients infected by non-genotype 1 HCV, particularly genotype 3. Indeed, in the golden era of direct-acting antiviral drugs, genotype 3 infections are no longer considered as easy to treat and are associated with higher risk of developing severe liver injuries, such as cirrhosis and hepatocellular carcinoma. Moreover, HCV genotype 3 accounts for 40% of all HCV infections in Asia and is the most frequent genotype among HCV-positive injecting drug users in several countries. Here, we review recent data on HCV genotype 3 infection/treatment, including clinical aspects and the underlying genotype-specific molecular mechanisms.

Establishment of a novel triple-transgenic mouse: conditionally and liver-specifically expressing hepatitis C virus NS3/4A protease

It is well known that NS3/4A protein plays crucial roles in the hepatitis C virus (HCV) replication. NS3/4A protein also results to virus-mediated immune evasion and persistence of infection through the interaction with host proteins. However, the lack of a suitable animal model hampers studies of HCV NS3/4A protein interaction with host proteins, which impacts immunopathology due to infection. Here, transgenic vector containing transcriptional regulation and Fluc reporter gene was constructed to conditionally express NS3/4A protein under the dual control of Tet-On regulatory system and Cre/LoxP gene-knockout system. NS3/4A transgenic founder mice were continuously crossed with Lap transgenic mice expressing reverse tetracycline-controlled transcriptional activator (rtTA), the NS3/4A/Lap double transgenic mouse lines with liver-specifically and conditionally expressing reporter (luciferase Fluc) under control of Tet-On system were established. The NS3/4A/Lap double transgenic mouse are mated with Lap/LC-1 double transgenic mouse with liver-specifically and conditionally expressing Cre recombinase under control of Tet-On system, NS3/4A/Lap/LC-1 triple transgenic mouse were generated. In vivo bioluminescent imaging, western blotting and immunohistochemical staining (IHS) was used to confirm that NS3/4A protein was strictly expressed in the liver of Doxycycline-induced triple transgenic mice. The results show that we established a triple-transgenic mouse model conditionally expressing the HCV NS3/4A protein under strict control of the Tet-On regulatory system and Cre/loxP system. This novel transgenic mouse model expressing NS3/4A in a temporally and spatially-specific manner will be useful for studying interactions between HCV NS3/4A protein and the host, also for evaluating NS3/4A protease inhibitors.

In vitro infection of primary human hepatocytes by HCV-positive sera: insights on a highly relevant model

OBJECTIVE

Adult primary human hepatocytes (PHHs) support the complete infection cycle of natural HCV from patients' sera. The molecular details underlying sera infectivity towards these cells remain largely unknown. Therefore, we sought to gain a deeper comprehension of these features in the most physiologically relevant culture system.

DESIGN

Using kinetic experiments, we defined the optimal conditions to infect PHH and explored the link between cell organisation and permissivity. Based on their infectivity, about 120 sera were classified in three groups. Concentration of 52 analytes was measured in 79 selected sera using multiplexed immunobead-based analyte profiling.

RESULTS

PHH permissivity towards HCV infection negatively correlated with cell polarisation and formation of functional bile canaliculi. PHH supported HCV replication for at least 2 weeks with de novo virus production. Depending on their reactivity, sera could be classified in three groups of high, intermediate or low infectivity toward PHH. Infectivity could not be predicted based on the donors' clinical characteristics, viral load or genotype. Interestingly, highly infectious sera displayed a specific cytokine profile with low levels of most of the 52 tested analytes. Among them, 24 cytokines/growth factors could impact hepatocyte biology and infection efficiency.

CONCLUSIONS

We identified critical factors leading to efficient PHH infection by HCV sera in vitro. Overall, we showed that this cellular model provides a useful tool for studying the mechanism of HCV infection in its natural host cell, selecting highly infectious isolates, and determining the potency of drugs towards various HCV strains.

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.

Heme and HO-1 Inhibition of HCV, HBV, and HIV

Hepatitis C virus, human immunodeficiency virus, and hepatitis B virus are chronic viral infections that cause considerable morbidity and mortality throughout the world. In the decades following the identification and sequencing of these viruses, in vitro experiments demonstrated that heme oxygenase-1, its oxidative products, and related compounds of the heme oxygenase system inhibit replication of all 3 viruses. The purpose of this review is to critically evaluate and summarize the seminal studies that described and characterized this remarkable behavior. It will also discuss more recent work that discovered the antiviral mechanisms and target sites of these unique antiviral agents. In spite of the fact that these viruses are diverse pathogens with quite profound differences in structure and life cycle, it is significant that heme and related compounds show striking similarity for viral target sites across all three species. Collectively, these findings strongly indicate that we should move forward and develop heme and related tetrapyrroles into versatile antiviral agents that could be used therapeutically in patients with single or multiple viral infections.

Matrigel-embedded 3D culture of Huh-7 cells as a hepatocyte-like polarized system to study hepatitis C virus cycle

Hepatocytes are highly polarized cells where intercellular junctions, including tight junctions (TJs), determine the polarity. Recently, the TJ-associated proteins claudin-1 and occludin have been implicated in hepatitis C virus (HCV) entry and spread. Nevertheless, cell line-based experimental systems that exhibit hepatocyte-like polarity and permit robust infection and virion production are not currently available. Thus, we sought to determine whether cell line-based, Matrigel-embedded cultures could be used to study hepatitis C virus (HCV) infection and virion production in a context of hepatocyte-like polarized cells. In contrast to standard bidimensional cultures, Matrigel-cultured Huh-7 cells adopted hepatocyte polarization features forming a continuous network of functional proto-bile canaliculi structures. These 3D cultures supported HCV infection by JFH-1 virus and produced infective viral particles which shifted towards lower densities with higher associated specific infectivity. In conclusion, our findings describe a novel use of Matrigel to study the entire HCV cycle in a more relevant context.

In vitro systems for the study of hepatitis C virus infection

The study of a virus is made possible by the availability of culture systems in which the viral lifecycle can be realized. Such systems support robust virus entry, replication, assembly, and secretion of nascent virions. Furthermore, culture models provide a platform in which therapeutic interventions can be devised or monitored. Hepatitis C virus (HCV) has a restricted tropism to human and chimpanzees; thus investigations of HCV biology have been hindered for many years due to a lack of small animal models. Nevertheless, significant efforts have been directed at developing cell culture models to elucidate the viral lifecycle in vitro. HCV primarily infects liver parenchymal cells commonly known as hepatocytes. The liver is a highly specialized and complex organ and the development of in vitro systems that reflects this complexity has proven difficult. Consequently, host cell receptor molecules that potentiate HCV infection were identified over a decade after the virus was discovered. A summary of the various HCV in vitro culture models, their advantages, and disadvantages are described.

Long-term propagation of serum hepatitis C virus (HCV) with production of enveloped HCV particles in human HepaRG hepatocytes

HepaRG human liver progenitor cells exhibit morphology and functionality of adult hepatocytes. We investigated the susceptibility of HepaRG hepatocytes to in vitro infection with serum-derived hepatitis C virus (HCV) particles (HCVsp) and the potential neutralizing activity of the E1E2-specific monoclonal antibody (mAb) D32.10. The infection was performed using HCVsp when the cells actively divided at day 3 postplating. HCV RNA, E1E2, and core antigens were quantified in HCV particles recovered from culture supernatants of differentiated cells for up to 66 days. The density distributions of particles were analyzed on iodixanol or sucrose gradients. Electron microscopy (EM) and immune-EM studies were performed for ultrastructural analysis of cells and localization of HCV E1E2 proteins in thin sections. HCV infection of HepaRG cells was documented by increasing production of E1E2-core-RNA(+) HCV particles from day 21 to day 63. Infectious particles sedimented between 1.06 and 1.12 g/mL in iodixanol gradients. E1E2 and core antigens were expressed in 50% of HCV-infected cells at day 31. The D32.10 mAb strongly inhibited HCV RNA production in HepaRG culture supernatants. Infected HepaRG cells frozen at day 56 were reseeded at low density. After only 1-3 subcultures and induction of a cell differentiation process the HepaRG cells produced high titer HCV RNA and thus showed to be sustainably infected. Apolipoprotein B-associated empty E1E2 and complete HCV particles were secreted. Characteristic virus-induced intracellular membrane changes and E1E2 protein-association to vesicles were observed.

CONCLUSION

HepaRG progenitor cells permit HCVsp infection. Differentiated HepaRG cells support long-term production of infectious lipoprotein-associated enveloped HCV particles. The E1E2-specific D32.10 mAb neutralizes the infection and this cellular model could be used as a surrogate infection system for the screening of entry inhibitors.

Interplay among cellular polarization, lipoprotein metabolism and hepatitis C virus entry

Hepatitis C virus (HCV) infects more than three million new individuals worldwide each year. In a high percentage of patients, acute infections become chronic, eventually progressing to fibrosis, cirrhosis, and hepatocellular carcinoma. Given the lack of effective prophylactic or therapeutic vaccines, and the limited sustained virological response rates to current therapies, new approaches are needed to prevent, control, and clear HCV infection. Entry into the host cell, being the first step of the viral cycle, is a potential target for the design of new antiviral compounds. Despite the recent discovery of the tight junction-associated proteins claudin-1 and occludin as HCV co-receptors, which is an important step towards the understanding of HCV entry, the precise mechanisms are still largely unknown. In addition, increasing evidence indicates that tools that are broadly employed to study HCV infection do not accurately reflect the real process in terms of viral particle composition and host cell phenotype. Thus, systems that more closely mimic natural infection are urgently required to elucidate the mechanisms of HCV entry, which will in turn help to design antiviral strategies against this part of the infection process.

An Assessment of the Use of Chimpanzees in Hepatitis C Research Past, Present and Future: 2. Alternative Replacement Methods

The use of chimpanzees in hepatitis C virus (HCV) research was examined in the report associated with this paper ( 1: Validity of the Chimpanzee Model), in which it was concluded that claims of past necessity of chimpanzee use were exaggerated, and that claims of current and future indispensability were unjustifiable. Furthermore, given the serious scientific and ethical issues surrounding chimpanzee experimentation, it was proposed that it must now be considered redundant — particularly in light of the demonstrable contribution of alternative methods to past and current scientific progress, and the future promise that these methods hold. This paper builds on this evidence, by examining the development of alternative approaches to the investigation of HCV, and by reviewing examples of how these methods have contributed, and are continuing to contribute substantially, to progress in this field. It augments the argument against chimpanzee use by demonstrating the comprehensive nature of these methods and the valuable data they deliver. The entire life-cycle of HCV can now be investigated in a human (and much more relevant) context, without recourse to chimpanzee use. This also includes the testing of new therapies and vaccines. Consequently, there is no sound argument against the changes in public policy that propose a move away from chimpanzee use in US laboratories.

Role for ADP ribosylation factor 1 in the regulation of hepatitis C virus replication

We hypothesized that ADP-ribosylation factor 1 (Arf1) plays an important role in the biogenesis and maintenance of infectious hepatitis C virus (HCV). Huh7.5 cells, in which HCV replicates and produces infectious viral particles, were exposed to brefeldin A or golgicide A, pharmacological inhibitors of Arf1 activation. Treatment with these agents caused a reduction in viral RNA levels, the accumulation of infectious particles within the cells, and a reduction in the levels of these particles in the extracellular medium. Fluorescence analyses showed that the viral nonstructural (NS) proteins NS5A and NS3, but not the viral structural protein core, shifted their localization from speckle-like structures in untreated cells to the rims of lipid droplets (LDs) in treated cells. Using pulldown assays, we showed that ectopic overexpression of NS5A in Huh7 cells reduces the levels of GTP-Arf1. Downregulation of Arf1 expression by small interfering RNA (siRNA) decreased both the levels of HCV RNA and the production of infectious viral particles and altered the localization of NS5A to the peripheries of LDs. Together, our data provide novel insights into the role of Arf1 in the regulation of viral RNA replication and the production of infectious HCV.

Association of anti-E1E2 antibodies with spontaneous recovery or sustained viral response to therapy in patients infected with hepatitis C virus

The monoclonal antibody (mAb) D32.10 recognizes a discontinuous epitope encompassing three regions E1 (amino acids 297-306), E2A (amino acids 480-494), and E2B (amino acids 613-621) juxtaposed on the surface of serum-derived hepatitis C virus (HCV) particles (HCVsp). The mAb D32.10 inhibits efficiently and specifically the binding of HCVsp to human hepatocytes. Therefore, we investigated the clinical relevance of anti-E1E2A,B response in the serum of patients infected with HCV. To this end, an enzyme-linked immunosorbent assay (ELISA) using synthetic E1-, E2A-, and E2B-derived peptides was used. The ELISA was validated in terms of sensitivity, specificity, and test efficiency. The detection of the anti-E1E2 D32.10 epitope-binding antibodies during natural HCV infection in more than 300 HCV-positive sera demonstrated significantly (P < 0.001) higher prevalence of these antibodies: (1) in patients who spontaneously cured HCV infection (46 of 52, 88.5%) showing high titers (70% ≥ 1/1000) compared to never-treated patients with chronic hepatitis C (7 of 50, 14%) who actively replicated the virus, and (2) in complete responders (20 of 52, 38.5%) who cleared virus following treatment and achieved a sustained viral response compared to nonresponders (4 of 40, 10%). Serum anti-E1E2 antibodies were monitored before, during, and after the current standard-of-care therapy (pegylated interferon plus ribavirin) in responder and nonresponder patients. Optimal cutoff values were assessed by receiver operating characteristic curve analysis. One month prior to therapy initiation, the threshold of 1131 (optical density × 1000) gave 100% and 86% positive and negative predictive values, respectively, for achieving or not achieving a sustained viral response.

CONCLUSION

The anti-E1E2 D32.10 epitope-binding antibodies are associated with control of HCV infection and may represent a new relevant prognostic marker in serum. This unique D32.10 mAb may also have immunotherapeutic potential.

Use of human hepatocytes to investigate HCV infection

Investigations on the biology of hepatitis C virus (HCV) have been hampered by the lack of small animal models. Efforts have therefore been directed to designing practical and robust cellular models of human origin able to support HCV replication and production in a reproducible and physiologically pertinent manner. Different systems have been constructed based on hepatoma or other cell lines, sub-genomic and genomic replicons, productive replicons, and immortalized hepatocytes. Although these models are practical for high-throughput screenings, they present several drawbacks related to the nature of the virions and the fact that the cells are not differentiated. Adult primary human hepatocytes infected with natural serum-derived HCV virions represent the model that most closely mimics the physiological situation. This chapter describes our experience with this culture model.

The cell biology of hepatitis C virus

Hepatitis C virus infects 3% of the world's population and has a variable disease course with potentially sever outcomes, liver failure and hepatocellular carcinoma. The influence of HCV the biology of infected hepatocytes is now just becoming known. This review will focus on effect of HCV on host cells.