Virology of hepatitis C virus

Mechanisms and Consequences of Genetic Variation in Hepatitis C Virus (HCV)

Chronic infection with hepatitis C virus (HCV) is an important contributor to the global incidence of liver diseases, including liver cirrhosis and hepatocellular carcinoma. Although common for single-stranded RNA viruses, HCV displays a remarkable high level of genetic diversity, produced primarily by the error-prone viral polymerase and host immune pressure. The high genetic heterogeneity of HCV has led to the evolution of several distinct genotypes and subtypes, with important consequences for pathogenesis, and clinical outcomes. Genetic variability constitutes an evasion mechanism against immune suppression, allowing the virus to evolve epitope escape mutants that avoid immune recognition. Thus, heterogeneity and variability of the HCV genome represent a great hindrance for the development of vaccines against HCV. In addition, the high genetic plasticity of HCV allows the virus to rapidly develop antiviral resistance mutations, leading to treatment failure and potentially representing a major hindrance for the cure of chronic HCV patients. In this chapter, we will present the central role that genetic diversity has in the viral life cycle and epidemiology of HCV. Incorporation errors and recombination, both the result of HCV polymerase activity, represent the main mechanisms of HCV evolution. The molecular details of both mechanisms have been only partially clarified and will be presented in the following sections. Finally, we will discuss the major consequences of HCV genetic diversity, namely its capacity to rapidly evolve antiviral and immunological escape variants that represent an important limitation for clearance of acute HCV, for treatment of chronic hepatitis C and for broadly protective vaccines.

An Insight into Hepatitis C Virus: In Search of Promising Drug Targets

Hepatitis C Virus (HCV) is a global health concern, chronically infecting over 70 million people worldwide. HCV is a bloodborne pathogen that primarily affects the liver, and chronic HCV infection can lead to cirrhosis, liver cancer, and liver failure over time. There is an urgent need for more effective approaches to prevent and treat HCV. This review summarizes current knowledge on the virology, transmission, diagnosis, and management of HCV infection. It also provides an in-depth analysis of HCV proteins as promising targets for antiviral drug and vaccine development. Specific HCV proteins discussed as potential drug targets include the NS5B polymerase, NS3/4A protease, entry receptors like CD81, and core proteins. The implications of HCV proteins as diagnostic and prognostic biomarkers are also explored. Current direct-acting antiviral therapies are effective but have cost, genotype specificity, and resistance limitations. This review aims to synthesize essential information on HCV biology and pathogenesis to inform future research on improved preventive, diagnostic, and therapeutic strategies against this global infectious disease threat.

The epidemiological profile of chronic hepatitis C with advanced hepatic fibrosis regarding virus genotype in Taiwan: A nationwide study

BACKGROUND/PURPOSE

This study aims at investigating the epidemiological profile of chronic hepatitis C (CHC) regarding hepatitis C virus (HCV) genotype in Taiwan.

METHODS

A total of 29,087 CHC patients with advanced fibrosis who received direct-acting antivirals (DAAs) therapy under Taiwan's National Health Insurance (NHI) during 2017-2018 were recruited. The HCV genotype distribution and its association with patients' demographic factors including age, gender, and geographical areas were examined.

RESULTS

The most common genotypes were 1b (59.5%) and 2 (30.1%) with characteristics of older age (mean ± standard deviation (SD): 66.5 ± 10.7 years and 67.3 ± 10.9 years) and female gender predominant (57.1% and 59.4%), which were associated with iatrogenic infection decades ago. Most of patients with genotype 1a (5.9%) and 6 (3.7%) infection were relatively younger (59.2 ± 12.0 years and 60.0 ± 13.8 years) and male gender predominant (59.1% and 61.1%), except Liujia and Liuying districts in southern Taiwan. The youngest group (53.2 ± 11.8 years) and most male gender predominant (74.3%) was genotype 3 (0.37%). These genotypes with characteristics of being younger and male gender predominant were highly related to injection drug use in recent years. The number of genotype 4 patients were extremely rare (n = 25) and efficacy of genotype-4-specific-DAA was significantly poorer than non-genotype-4-specific DAA (P value = 0.0411).

CONCLUSION

The significant differences in demographic characteristics among CHC patients with different HCV genotypes found in this study suggest HCV genotype was highly associated with transmission pattern and may be used as a reference for HCV control.

Hepatitis C virus-host interactions: Etiopathogenesis and therapeutic strategies

Hepatitis C virus (HCV) is a significant health problem facing the world. This virus infects more than 170 million people worldwide and is considered the major cause of both acute and chronic hepatitis. Persons become infected mainly through parenteral exposure to infected material by blood transfusions or injections with nonsterile needles. Although the sexual behavior is considered as a high risk factor for HCV infection, the transmission of HCV infection through sexual means, is less frequently. Currently, the available treatment for patients with chronic HCV infection is interferon based therapies alone or in combination with ribavirin and protease inhibitors. Although a sustained virological response of patients to the applied therapy, a great portion of patients did not show any response. HCV infection is mostly associated with progressive liver diseases including fibrosis, cirrhosis and hepatocellular carcinoma. Although the focus of many patients and clinicians is sometimes limited to that problem, the natural history of HCV infection (HCV) is also associated with the development of several extrahepatic manifestations including dermatologic, rheumatologic, neurologic, and nephrologic complications, diabetes, arterial hypertension, autoantibodies and cryglobulins. Despite the notion that HCV-mediated extrahepatic manifestations are credible, the mechanism of their modulation is not fully described in detail. Therefore, the understanding of the molecular mechanisms of HCV-induced alteration of intracellular signal transduction pathways, during the course of HCV infection, may offer novel therapeutic targets for HCV-associated both hepatic and extrahepatic manifestations. This review will elaborate the etiopathogenesis of HCV-host interactions and summarize the current knowledge of HCV-associated diseases and their possible therapeutic strategies.

Morphogenesis of infectious hepatitis C virus particles

More than 170 million individuals are currently infected with hepatitis C virus (HCV) worldwide and are at continuous risk of developing chronic liver disease. Since a cell culture system enabling relatively efficient propagation of HCV has become available, an increasing number of viral and host factors involved in HCV particle formation have been identified. Association of the viral Core, which forms the capsid with lipid droplets appears to be prerequisite for early HCV morphogenesis. Maturation and release of HCV particles is tightly linked to very-low-density lipoprotein biogenesis. Although expression of Core as well as E1 and E2 envelope proteins produces virus-like particles in heterologous expression systems, there is increasing evidence that non-structural viral proteins and p7 are also required for the production of infectious particles, suggesting that HCV genome replication and virion assembly are closely linked. Advances in our understanding of the various molecular mechanisms by which infectious HCV particles are formed are summarized.

Oncogenic potential of hepatitis C virus proteins

Chronic hepatitis C virus (HCV) infection is a major risk factor for liver disease progression, and may lead to cirrhosis and hepatocellular carcinoma (HCC). The HCV genome contains a single-stranded positive sense RNA with a cytoplasmic lifecycle. HCV proteins interact with many host-cell factors and are involved in a wide range of activities, including cell cycle regulation, transcriptional regulation, cell proliferation, apoptosis, lipid metabolism, and cell growth promotion. Increasing experimental evidences suggest that HCV contributes to HCC by modulating pathways that may promote malignant transformation of hepatocytes. At least four of the 10 HCV gene products, namely core, NS3, NS5A and NS5B play roles in several potentially oncogenic pathways. Induction of both endoplasmic reticulum (ER) stress and oxidative stress by HCV proteins may also contribute to hepatocyte growth promotion. The current review identifies important functions of the viral proteins connecting HCV infections and potential for development of HCC. However, most of the putative transforming potentials of the HCV proteins have been defined in artificial cellular systems, and need to be established relevant to infection and disease models. The new insight into the mechanisms for HCV mediated disease progression may offer novel therapeutic targets for one of the most devastating human malignancies in the world today.

A 24-week course of high-dose interferon-alpha plus ribavirin for Taiwanese chronic hepatitis C patients with persistently normal or near-normal alanine aminotransferase levels

BACKGROUND/AIMS

We aimed to evaluate the efficacy, advantage, and safety of a 24-week regimen with high-dose interferon-alpha (INF-alpha; 6 million units thrice weekly) plus ribavirin (1000-1200 mg/day) combination therapy for 46 Taiwanese chronic hepatitis C (CHC) patients with persistently normal or near-normal alanine aminotransferase (PNALT) levels.

METHODS

Ninety-two age- and sex-matched CHC patients with elevated ALT levels (> 2 times the upper limit of normal range) with a ratio of 1:2, treated with the same regimen, served as a control.

RESULTS

The sustained virologic response (SVR) rate was comparable between PNALT (67.4%) and elevated ALT (65.2%) groups (intention-to-treat analysis). The two groups had similar rates of discontinuation and incidence of adverse effects. Viral genotype 1b, baseline viral loads, body mass index, and age were significant factors negatively associated with SVR. Further decline of ALT levels throughout the follow-up period was observed in sustained responders of the PNALT group. None of the eight patients with ALT flares developed icteric hepatitis. The virologic efficacy was sustained in a 3-year extended follow-up period.

CONCLUSION

high-dose INF-alpha with ribavirin combination therapy is effective, safe, and well tolerated in CHC patients with PNALT levels. The ALT assay might not be used as a single biochemical marker for determination of treatment consideration.

Novel nonnucleoside inhibitor of hepatitis C virus RNA-dependent RNA polymerase

A novel nonnucleoside inhibitor of hepatitis C virus (HCV) RNA-dependent RNA polymerase (RdRp), [(1R)-5-cyano-8-methyl-1-propyl-1,3,4,9-tetrahydropyano[3,4-b]indol-1-yl] acetic acid (HCV-371), was discovered through high-throughput screening followed by chemical optimization. HCV-371 displayed broad inhibitory activities against the NS5B RdRp enzyme, with 50% inhibitory concentrations ranging from 0.3 to 1.8 microM for 90% of the isolates derived from HCV genotypes 1a, 1b, and 3a. HCV-371 showed no inhibitory activity against a panel of human polymerases, including mitochondrial DNA polymerase gamma, and other unrelated viral polymerases, demonstrating its specificity for the HCV polymerase. A single administration of HCV-371 to cells containing the HCV subgenomic replicon for 3 days resulted in a dose-dependent reduction of the steady-state levels of viral RNA and protein. Multiple treatments with HCV-371 for 16 days led to a >3-log10 reduction in the HCV RNA level. In comparison, multiple treatments with a similar inhibitory dose of alpha interferon resulted in a 2-log10 reduction of the viral RNA level. In addition, treatment of cells with a combination of HCV-371 and pegylated alpha interferon resulted in an additive antiviral activity. Within the effective antiviral concentrations of HCV-371, there was no effect on cell viability and metabolism. The intracellular antiviral specificity of HCV-371 was demonstrated by its lack of activity in cells infected with several DNA or RNA viruses. Fluorescence binding studies show that HCV-371 binds the NS5B with an apparent dissociation constant of 150 nM, leading to high selectivity and lack of cytotoxicity in the antiviral assays.

Detection of active hepatitis C virus and hepatitis G virus/GB virus C replication in bone marrow in human subjects

We have analyzed the presence of hepatitis C virus (HCV) and hepatitis G virus (HGV) sequences in bone marrow and serum samples from 48 patients of a hematologic outpatient clinic. HCV RNA was detected in 18 (38%) and 15 (31%) and HGV RNA was detected in 6 (13%) and 9 (19%) of serum and bone marrow samples, respectively. In 3 patients, HGV RNA was detectable in bone marrow but not in the serum; 2 of these patients were negative for the presence of specific antibodies. Using a highly strand-specific Tth-based reverse transcriptase-polymerase chain reaction (RT-PCR), the presence of HCV RNA and HGV RNA negative strand was demonstrated in 4 and 5 bone marrow samples, respectively. Our study shows that HCV and HGV can replicate in bone marrow; in the case of HGV, analysis of serum may underestimate the true prevalence of infection.

Detection of active hepatitis C virus and hepatitis G virus/GB virus C replication in bone marrow in human subjects

We have analyzed the presence of hepatitis C virus (HCV) and hepatitis G virus (HGV) sequences in bone marrow and serum samples from 48 patients of a hematologic outpatient clinic. HCV RNA was detected in 18 (38%) and 15 (31%) and HGV RNA was detected in 6 (13%) and 9 (19%) of serum and bone marrow samples, respectively. In 3 patients, HGV RNA was detectable in bone marrow but not in the serum; 2 of these patients were negative for the presence of specific antibodies. Using a highly strand-specific Tth-based reverse transcriptase-polymerase chain reaction (RT-PCR), the presence of HCV RNA and HGV RNA negative strand was demonstrated in 4 and 5 bone marrow samples, respectively. Our study shows that HCV and HGV can replicate in bone marrow; in the case of HGV, analysis of serum may underestimate the true prevalence of infection.

A novel recombinant single-chain hepatitis C virus NS3-NS4A protein with improved helicase activity

Hepatitis C virus (HCV) nonstructural protein 3 (NS3) has been shown to possess protease and helicase activities and has also been demonstrated to spontaneously associate with nonstructural protein NS4A (NS4A) to form a stable complex. Previous attempts to produce the NS3/NS4A complex in recombinant baculovirus resulted in a protein complex that aggregated and precipitated in the absence of nonionic detergent and high salt. A single-chain form of the NS3/NS4A complex (His-NS4A21-32-GSGS-NS3-631) was constructed in which the NS4A core peptide is fused to the N-terminus of the NS3 protease domain as previously described (Taremi et al., 1998). This protein contains a histidine tagged NS4A peptide (a.a. 21-32) fused to the full-length NS3 (a.a. 3-631) through a flexible tetra amino acid linker. The recombinant protein was expressed to high levels in Escherichia coli, purified to homogeneity, and examined for NTPase, nucleic acid unwinding, and proteolytic activities. The single-chain recombinant NS3-NS4A protein possesses physiological properties equivalent to those of the NS3/NS4A complex except that this novel construct is stable, soluble and sixfold to sevenfold more active in unwinding duplex RNA. Comparison of the helicase activity of the single-chain recombinant NS3-NS4A with that of the full-length NS3 (without NS4A) and that of the helicase domain alone suggested that the presence of the protease domain and at least the NS4A core peptide are required for optimal unwinding activity.

Construction, expression, and characterization of a novel fully activated recombinant single-chain hepatitis C virus protease

Efficient proteolytic processing of essential junctions of the hepatitis C virus (HCV) polyprotein requires a heterodimeric complex of the NS3 bifunctional protease/helicase and the NS4A accessory protein. A single-chain recombinant form of the protease has been constructed in which NS4A residues 21-32 (GSVVIVGRIILS) were fused in frame to the amino terminus of the NS3 protease domain (residues 3-181) through a tetrapeptide linker. The single-chain recombinant protease has been overexpressed as a soluble protein in E. coli and purified to homogeneity by a combination of metal chelate and size-exclusion chromatography. The single-chain recombinant protease domain shows full proteolytic activity cleaving the NS5A-5B synthetic peptide substrate, DTEDVVCCSMSYTWTGK with a Km and k(cat) of 20.0 +/- 2.0 microM and 9.6 +/- 2.0 min(-1), respectively; parameters identical to those of the authentic NS3(1-631)/NS4A(1-54) protein complex generated in eukaryotic cells (Sali DL et al., 1998, Biochemistry 37:3392-3401).

Rapid genotyping of hepatitis C virus by direct cycle sequencing of PCR-amplified cDNAs and capillary electrophoresis analysis

There is an increasing demand for the genotyping of hepatitis C virus (HCV), since it has been shown that different HCV genotypes are associated with distinct profiles of pathogenicity and responses to antiviral treatment. Hence, there is a need for a simple and precise genotyping assay for routine diagnosis of HCV types and subtypes. Here we show that direct sequencing, considered as the reference method, can provide an accurate and rapid method for large-scale screening of HCV genotypes. PCR-amplified cDNAs of the HCV 5' non-coding region (5' NCR) were obtained from the widespread "Amplicor" HCV detection system. Semi-purified PCR products were directly cycle-sequenced in a single tube using multicolour dye terminator chemistry. Sample loading, electrophoresis and sequence analysis were automatically achieved by a capillary electrophoresis-based genetic analyser. Out of a total of 500 samples, HCV subtype 1b accounted for the majority of the infections (41%), followed by HCV 3 (31%) and HCV 1a (22%). This procedure failed to identify a genotype in only 3 samples. In addition, several cases of mixed HCV infection were also documented. The combination of direct cycle sequencing of PCR products with capillary electrophoresis provides a simple and rapid method convenient for routine HCV genotyping analysis.

Prevalence of hepatitis C virus in plasma pools and the effectiveness of cold ethanol fractionation

Screening blood donations for antibodies against hepatitis C virus (HCV) greatly reduces the risk of transmitting HCV by transfusions. However, despite such screening programs, plasma pools still contain a high percentage of HCV ribonucleic acid as determined by polymerase chain reaction. This result would not be alarming if the procedures for producing blood products included steps to inactivate or remove HCV. Although this appeared to be the case for all blood products, such as coagulation factors and most immunoglobulins, which are subjected to an inactivation step, the effectiveness of the cold ethanol fractionation process still needed to be determined. In validation experiments using bovine viral diarrhea virus as a model virus for HCV, we demonstrated that the Cohn-Oncley cold ethanol fractionation process neither inactivated nor removed this virus sufficiently. Our observations may help to explain how HCV was transmitted to a number of recipients of intravenous immunoglobulin.