Hepatitis C virus infection: in vivo and in vitro models

Marmosets as models of infectious diseases

Animal models of infectious disease often serve a crucial purpose in obtaining licensure of therapeutics and medical countermeasures, particularly in situations where human trials are not feasible, i.e., for those diseases that occur infrequently in the human population. The common marmoset (Callithrix jacchus), a Neotropical new-world (platyrrhines) non-human primate, has gained increasing attention as an animal model for a number of diseases given its small size, availability and evolutionary proximity to humans. This review aims to (i) discuss the pros and cons of the common marmoset as an animal model by providing a brief snapshot of how marmosets are currently utilized in biomedical research, (ii) summarize and evaluate relevant aspects of the marmoset immune system to the study of infectious diseases, (iii) provide a historical backdrop, outlining the significance of infectious diseases and the importance of developing reliable animal models to test novel therapeutics, and (iv) provide a summary of infectious diseases for which a marmoset model exists, followed by an in-depth discussion of the marmoset models of two studied bacterial infectious diseases (tularemia and melioidosis) and one viral infectious disease (viral hepatitis C).

Reprint of: Coronavirus reverse genetic systems: infectious clones and replicons

Coronaviruses (CoVs) infect humans and many animal species, and are associated with respiratory, enteric, hepatic, and central nervous system diseases. The large size of the CoV genome and the instability of some CoV replicase gene sequences during its propagation in bacteria, represent serious obstacles for the development of reverse genetic systems similar to those used for smaller positive sense RNA viruses. To overcome these limitations, several alternatives to more conventional plasmid-based approaches have been established in the last 13 years. In this report, we briefly review and discuss the different reverse genetic systems developed for CoVs, paying special attention to the severe acute respiratory syndrome CoV (SARS-CoV).

Coronavirus reverse genetic systems: infectious clones and replicons

Coronaviruses (CoVs) infect humans and many animal species, and are associated with respiratory, enteric, hepatic, and central nervous system diseases. The large size of the CoV genome and the instability of some CoV replicase gene sequences during its propagation in bacteria, represent serious obstacles for the development of reverse genetic systems similar to those used for smaller positive sense RNA viruses. To overcome these limitations, several alternatives to more conventional plasmid-based approaches have been established in the last 13 years. In this report, we briefly review and discuss the different reverse genetic systems developed for CoVs, paying special attention to the severe acute respiratory syndrome CoV (SARS-CoV).

Hepatitis C virus infection of a thyroid cell line: implications for pathogenesis of hepatitis C virus and thyroiditis

BACKGROUND

Autoimmune and non-autoimmune thyroiditis frequently occur in persons with hepatitis C virus (HCV) infection. Treatment with interferon alpha (IFNα) is also associated with significant risk for the development of thyroiditis. To explore HCV-thyroid interactions at a cellular level, we evaluated whether a human thyroid cell line (ML1) could be infected productively with HCV in vitro.

METHODS AND RESULTS

ML1 cells showed robust surface expression of the major HCV receptor CD81. Using a highly sensitive, strand-specific reverse transcription polymerase chain reaction assay, positive-sense and negative-sense HCV RNA were detected in ML1 cell lysates at days 3, 7, and 14 postinfection with HCV. HCV core protein was expressed at high levels in ML1 supernatants at days 1, 3, 5, 7, and 14 postinfection. The nonstructural protein NS5A was also detected in ML1 cell lysates by Western blotting. HCV entry into ML1 cells was shown to be dependent on the HCV entry factors CD81 and SR-B1/CLA1, while IFNα inhibited HCV replication in ML1 cells in a dose-dependent manner. Supernatants from HCV-infected ML1 cells were able to infect fresh ML1 cells productively, suggesting that infectious virions could be transferred from infected to naïve thyroid cells in vivo. Additionally, HCV infection of ML1 cells led to increased expression of the pro-inflammatory cytokine IL-8.

CONCLUSIONS

For the first time, we have demonstrated that HCV can infect human thyroid cells in vitro. These findings strongly suggest that HCV infection of thyrocytes may play a role in the association between chronic HCV infection and thyroid autoimmunity. Furthermore, the thyroid may serve as an extrahepatic reservoir for HCV viral replication, thus contributing to the persistence of viral infection and to the development of thyroid autoimmunity.

The interaction between HCV and nuclear receptor-mediated pathways

Hepatitis C virus (HCV) is presently the leading indication for liver transplantation in Western countries. Treatment for HCV infection includes a combination of pegylated interferon and ribavirin, which produces highly variable response rates. This reflects the lack of information regarding the roles of host and viral components during viral pathogenesis. Vital processes regulated by the liver, including metabolism, lipid homeostasis, cellular proliferation, and the immune response, are known to be systematically dysregulated as a result of persistent HCV infection. Nuclear receptors and their ligands are recognized as indispensable regulators of liver homeostasis. Pathways mediated by the nuclear receptor superfamily have been shown to be profoundly disrupted during HCV infection, leading to an increased importance in elucidating the exact nature of this complex relationship. Expanded understanding of the role of nuclear receptors in HCV infection may therefore be an essential step in the search for a more universally effective treatment.

Dendritic cells in hepatitis C infection: can they (help) win the battle?

Infection with hepatitis C virus (HCV) is a public health problem; it establishes a chronic course in ~85% of infected patients and increases their risk for developing liver cirrhosis, hepatocellular carcinoma, and significant extrahepatic manifestations. The mechanisms of HCV persistence remain elusive and are largely related to inefficient clearance of the virus by the host immune system. Dendritic cells (DCs) are the most efficient inducers of immune responses; they are capable of triggering productive immunity and maintaining the state of tolerance to self- and non-self antigens. During the past decade, multiple research groups have focused on DCs, in hopes of unraveling an HCV-specific DC signature or DC-dependent mechanisms of antiviral immunity which would lead to a successful HCV elimination strategy. This review incorporates the latest update in the current status of knowledge on the role of DCs in anti-HCV immunity as it relates to several challenging questions: (a) the phenotype and function of diverse DC subsets in HCV-infected patients; (b) the characteristics of non-human HCV infection models from the DCs' point of view; (c) how can in vitro systems, ranging from HCV protein- or peptide-exposed DC to HCV protein-expressing DCs, and in vivo systems, ranging from HCV protein-expressing transgenic mice to HCV-infected non-human primates, be employed to dissect the role of DCs in triggering/maintaining a robust antiviral response; and (d) the prospect of DC-based strategy for managing and finding a cure for HCV infection.

Hepatic differentiation of human embryonic stem cells is promoted by three-dimensional dynamic perfusion culture conditions

The developmental potential of human embryonic stem cells (hESCs) holds great promise to provide a source of human hepatocytes for use in drug discovery, toxicology, hepatitis research, and extracorporeal bioartificial liver support. There are, however, limitations to induce fully functional hepatocytes on conventional two-dimensional (2D) static culture. It had been shown that dynamic three-dimensional (3D) perfusion culture is superior to induce maturation in fetal hepatocytes and prolong hepatic functions of primary adult hepatocytes. We investigated the potential of using a four-compartment 3D perfusion culture to induce hepatic differentiation in hESC. Undifferentiated hESC were inoculated into hollow fiber-based 3D perfusion bioreactors with integral oxygenation. Hepatic differentiation was induced with a multistep growth factor cocktail protocol. Parallel controls were operated under equal perfusion conditions without the growth factor supplementations to allow for spontaneous differentiation, as well as in conventional 2D static conditions using growth factors. Metabolism, hepatocyte-specific gene expression, protein expression, and hepatic function were evaluated after 20 days. Significantly upregulated hepatic gene expression was observed in the hepatic differentiation 3D culture group. Ammonia metabolism activity and albumin production was observed in the 3D directed differentiation culture. Drug-induced cytochrome P450 gene expression was increased with rifampicin induction. Using flow cytometry analysis the mature hepatocyte marker asialoglycoprotein receptor was found on up to 30% of the cells in the 3D system with directed hepatic differentiation. Histological and immunohistochemical analysis revealed structural formation of hepatic and biliary marker-positive cells. In contrast to 2D culture, the 3D perfusion culture induced more functional maturation in hESC-derived hepatic cells. 3D perfusion bioreactor technologies may be useful for further studies on generating hESC-derived hepatic cells.

An assessment of the use of chimpanzees in hepatitis C research past, present and future: 1. Validity of the chimpanzee model

The USA is the only significant user of chimpanzees in biomedical research in the world, since many countries have banned or limited the practice due to substantial ethical, economic and scientific concerns. Advocates of chimpanzee use cite hepatitis C research as a major reason for its necessity and continuation, in spite of supporting evidence that is scant and often anecdotal. This paper examines the scientific and ethical issues surrounding chimpanzee hepatitis C research, and concludes that claims of the necessity of chimpanzees in historical and future hepatitis C research are exaggerated and unjustifiable, respectively. The chimpanzee model has several major scientific, ethical, economic and practical caveats. It has made a relatively negligible contribution to knowledge of, and tangible progress against, the hepatitis C virus compared to non-chimpanzee research, and must be considered scientifically redundant, given the array of alternative methods of inquiry now available. The continuation of chimpanzee use in hepatitis C research adversely affects scientific progress, as well as chimpanzees and humans in need of treatment. Unfounded claims of its necessity should not discourage changes in public policy regarding the use of chimpanzees in US laboratories.

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.

Hepatitis C virus genomic RNA dimerization is mediated via a kissing complex intermediate

With over 200 million people infected with hepatitis C virus (HCV) worldwide, there is a need for more effective and better-tolerated therapeutic strategies. The HCV genome is a positive-sense; single-stranded RNA encoding a large polyprotein cleaved at multiple sites to produce at least ten proteins, among them an error-prone RNA polymerase that confers a high mutation rate. Despite considerable overall sequence diversity, in the 3'-untranslated region of the HCV genomic RNA there is a 98-nucleotide (nt) sequence named X RNA, the first 55 nt of which (X55 RNA) are 100% conserved among all HCV strains. The X55 region has been suggested to be responsible for in vitro dimerization of the genomic RNA in the presence of the viral core protein, although the mechanism by which this occurs is unknown. In this study, we analyzed the X55 region and characterized the mechanism by which it mediates HCV genomic RNA dimerization. Similar to a mechanism proposed previously for the human immunodeficiency 1 virus (HIV-1) genome, we show that dimerization of the HCV genome involves formation of a kissing complex intermediate, which is converted to a more stable extended duplex conformation in the presence of the core protein. Mutations in the dimer linkage sequence loop sequence that prevent RNA dimerization in vitro significantly reduced but did not completely ablate the ability of HCV RNA to replicate or produce infectious virus in transfected cells.

Advances in understanding the role of HCV proteins in the pathogenesis of HCV-induced liver diseases in animal models

Hepatitis C virus (HCV) is closely associated with the occurrence of hepatitis, cirrhosis and liver cancer. As HCV naturally infects only humans and higher primates, few animal models of HCV infection have been established. As a result, limited knowledge on the pathophysiology of and host immune responses to HCV infection is obtained. Gene transfer approaches have been used to establish relevant animal models to investigate the molecular basis of HCV-induced liver diseases. This paper focuses on providing an overview of the recent advances in understanding the role of HCV proteins in the pathogenesis of HCV-induced liver diseases in animal models.

Antiviral therapy for hepatitis C virus: beyond the standard of care

Hepatitis C virus (HCV) represents a major health burden, with an estimated 180 million chronically infected individuals worldwide. These patients are at increased risk of developing liver cirrhosis and hepatocellular carcinoma. Infection with HCV is the leading cause of liver transplantation in the Western world. Currently, the standard of care (SoC) consists of pegylated interferon alpha (pegIFN-α) and ribavirin (RBV). However this therapy has a limited efficacy and is associated with serious side effects. Therefore more tolerable, highly potent inhibitors of HCV replication are urgently needed. Both Specifically Targeted Antiviral Therapy for HCV (STAT-C) and inhibitors that are believed to interfere with the host-viral interaction are discussed.

Effects of HCV proteins in current HCV transgenic models

Hepatits C virus (HCV) is an enveloped virus with positive-sense single-stranded RNA genome that causes both acute and persistent infections associated with chronic hepatitis, cirrhosis and hepatocellular carcinoma, which needs fully functional human hepatocytes for its development. Due to the strict human tropism of HCV, only human and higher primates such as chimpanzees have been receptive to HCV infection and development, cognition about pathophysiololgy and host immune responses of HCV infection is limited by lacking of simple laboratory models of infection for a long time. During the past decade, gene transfer approaches have been helpful to the understanding of the molecular basis of human disease. Transgenic cell lines, chimeric and transgenic animal models were developed and had been demonstrated their invaluable benefits. This review focuses on the existing HCV transgenic models and summarize the relative results about probable pathophysical changes induced by HCV proteins.

Chronic hepatitis C virus infection associated with autonomic dysfunction

BACKGROUND

Impaired autonomic function has been described in patients with chronic liver diseases from different aetiologies, and has proven to be a poor prognostic indicator. To date, it is not known how chronic hepatitis C virus (HCV) infection affects the autonomic nervous system.

AIMS

In the present study, we compared cardiovagal autonomic function in patients with chronic HCV infection and healthy controls and examined the relation between autonomic function and serum levels of aminotransferases, HCV RNA, cryoglobulins, albumin and glucose.

METHODS

Autonomic function was assessed in 45 treatment-naïve patients with chronic HCV infection and in 40 healthy controls by determining spontaneous baroreflex sensitivity (BRS) and heart rate variability (HRV) indices. The R-R interval was determined by electrocardiogram recording; continuous radial artery pressure was monitored simultaneously by applanation tonometry. Laboratory analyses and quantitative polymerase chain reaction for serum HCV RNA level were performed by standard procedures.

RESULTS

BRS and HRV time and frequency domain indices were lower in patients with HCV infection compared with healthy controls [7.1+/-3.4 vs. 11.5+/-6.5 ms/mmHg for BRS, 168.5+/-160.9 vs. 370.7+/-349.4 ms(2) for low-frequency HRV (mean+/-SD); P<0.01]. Multivariate analysis showed that autonomic dysfunction in HCV-infected patients correlated with elevated alanine aminotransferase levels, but was not associated with serum HCV RNA levels and cryoglobulins.

CONCLUSION

Our results suggest that impaired autonomic function is caused by chronic HCV infection. Further studies are needed, however, to identify the underlying mechanisms.