Reliance of host cholesterol metabolic pathways for the life cycle of hepatitis C virus

Hepatitis C virus cell entry: role of lipoproteins and cellular receptors

Hepatitis C virus (HCV), a major cause of chronic liver disease, is a single-stranded positive sense virus of the family Flaviviridae. HCV cell entry is a multi-step process, involving several viral and cellular factors that trigger virus uptake into the hepatocyte. Tetraspanin CD81, human scavenger receptor SR-BI, and tight junction molecules Claudin-1 and occludin are the main receptors that mediate HCV entry. In addition, the virus may use glycosaminoglycans and/or low density receptors on host cells as initial attachment factors. A unique feature of HCV is the dependence of virus replication and assembly on host cell lipid metabolism. Most notably, during HCV assembly and release from the infected cells, virus particles associate with lipids and very-low-density lipoproteins. Thus, infectious virus circulates in patient sera in the form of triglyceride-rich particles. Consequently, lipoproteins and lipoprotein receptors play an essential role in virus uptake and the initiation of infection. This review summarizes the current knowledge about HCV receptors, mechanisms of HCV cell entry and the role of lipoproteins in this process.

Association of lipid profiles with hepatitis C viral load in chronic hepatitis C patients with genotype 1 or 2 infection

OBJECTIVES

Metabolic profiles correlate with hepatitis C virus (HCV) infection and are known to be predictors of virologic responses in chronic hepatitis C patients on interferon-based treatment. However, little is known about the differential association of lipid profiles with hepatitis C viral load between genotype 1 and 2 infections. The aim of this study was to evaluate the impact of lipid profiles on HCV RNA levels in patients with genotypes 1 and 2.

METHODS

A total of 531 chronic hepatitis C patients infected patients with HCV genotype 1 or 2 were consecutively enrolled. Univariate and multivariate approaches were used to estimate the associations between demographic, metabolic, and viral variables and HCV RNA levels.

RESULTS

Higher serum triglyceride, total cholesterol, and low-density lipoprotein levels correlated with higher HCV RNA levels. In multivariate analysis, genotype 1 infection, severe hepatitis activity, milder hepatic fibrosis, higher homeostasis model assessment of insulin resistance (HOMA-IR) index and triglyceride levels are associated with higher HCV viral loads (P<0.05). Subanalysis on patients with lower body mass index values showed higher HCV viral load was associated with higher HOMA-IR index and total cholesterol level (P<0.05). After stratification by HCV genotype, lipid profiles were significantly associated with HCV viral load in genotype 2 infection (P<0.05), but not genotype 1 infection.

CONCLUSIONS

A proportional relationship is found between serum lipid profiles and hepatitis C viral load in patients with genotype 2 infection; however, whether manipulation of lipid profiles would improve the response to current anti-HCV therapy is to be determined in further studies.

Development and characterization of hepatitis C virus genotype 1-7 cell culture systems: role of CD81 and scavenger receptor class B type I and effect of antiviral drugs

Six major hepatitis C virus (HCV) genotypes and numerous subtypes have been described, and recently a seventh major genotype was discovered. Genotypes show significant molecular and clinical differences, such as differential response to combination therapy with interferon-alpha and ribavirin. Recently, HCV research has been accelerated by cell culture systems based on the unique growth capacity of strain JFH1 (genotype 2a). By development of JFH1-based intergenotypic recombinants containing Core, envelope protein 1 and 2 (E1, E2), p7, and nonstructural protein 2 (NS2) of genotype 6a and 7a strains, as well as subtype 1b and 2b strains, we have completed a panel of culture systems for all major HCV genotypes. Efficient growth in Huh7.5 cells depended on adaptive mutations for HK6a/JFH1 (6a/2a, in E1 and E2) and J4/JFH1 (1b/2a, in NS2 and NS3); viability of J8/JFH1 (2b/2a) and QC69/JFH1 (7a/2a) did not require adaptation. To facilitate comparative studies, we generated virus stocks of genotype 1-7 recombinants with infectivity titers of 10(3.7) to 10(5.2) 50% tissue culture infectious dose/mL and HCV RNA titers of 10(7.0) to 10(7.9) IU/mL. Huh7.5 cultures infected with genotype 1-6 viruses had similar spread kinetics, intracellular Core, NS5A, and lipid amounts, and colocalization of Core and NS5A with lipids. Treatment with interferon-alpha2b but not ribavirin or amantadine showed a significant antiviral effect. Infection with all genotypes could be blocked by specific antibodies against the putative coreceptors CD81 and scavenger receptor class B type I in a dose-dependent manner. Finally, neutralizing antibodies in selected chronic phase HCV sera had differential effects against genotype 1-7 viruses.

CONCLUSION

We completed and characterized a panel of JFH1-based cell culture systems of all seven major HCV genotypes and important subtypes and used these viruses in comparative studies of antivirals, HCV receptor interaction, and neutralizing antibodies.

Placebo-controlled trial of 400 mg amantadine combined with peginterferon alfa-2a and ribavirin for 48 weeks in chronic hepatitis C virus-1 infection

The impact of amantadine on virologic response rates of interferon-based treatment of chronic hepatitis C is controversial. The aim of this study was to compare virological response rates in patients with chronic hepatitis C virus (HCV)-1 infection treated with 400 mg amantadine or placebo in combination with peginterferon alfa-2a (40 kD) and ribavirin for 48 weeks. Seven hundred four previously untreated chronically HCV-1-infected patients (mean age, 46 +/- 12 years) were randomized to (A) amantadine-sulphate (400 mg/day) (n = 352) or (B) placebo (n = 352), both in combination with 180 microg peginterferon alfa-2a once weekly and ribavirin (1000-1200 mg/day) for 48 weeks. End of treatment and sustained virological response after a 24-week follow-up period were assessed by qualitative reverse transcription polymerase chain reaction (RT-PCR) (sensitivity, 50 IU/mL). Demographic and baseline virological parameters were similar in both treatment groups. In groups A and B, 231 of 352 patients (66%) and 256 of 352 patients (72%) achieved an end of treatment response, and 171 of 352 patients (49 %) and 186 of 352 patients (53 %) a sustained virological response, respectively. On-treatment dropout rate in the amantadine group was significantly higher than in the placebo group (32% versus 23%; P = 0.01). However, adverse events and laboratory abnormalities were similar between both groups. Per-protocol analysis revealed similar sustained virological response rates in both treatment groups (53% versus 55%).

CONCLUSION

In this large placebo-controlled multicenter study, amantadine even at a dose of 400 mg/day did not improve virological response rates of peginterferon alfa-2a and ribavirin in patients with chronic genotype HCV-1 infection.

Cutting the gordian knot-development and biological relevance of hepatitis C virus cell culture systems

Worldwide approximately 180 million people are chronically infected with hepatitis C virus (HCV). HCV isolates exhibit extensive genetic heterogeneity and have been grouped in six genotypes and various subtypes. Additionally, several naturally occurring intergenotypic recombinants have been described. Research on the viral life cycle, efficient therapeutics, and a vaccine has been hampered by the absence of suitable cell culture systems. The first system permitting studies of the full viral life cycle was intrahepatic transfection of RNA transcripts of HCV consensus complementary DNA (cDNA) clones into chimpanzees. However, such full-length clones were not infectious in vitro. The development of the replicon system and HCV pseudo-particles allowed in vitro studies of certain aspects of the viral life cycle, RNA replication, and viral entry, respectively. Identification of the genotype 2 isolate JFH1, which for unknown reasons showed an exceptional replication capability and resulted in formation of infectious viral particles in the human hepatoma cell line Huh7, led in 2005 to the development of the first full viral life cycle in vitro systems. JFH1-based systems now enable in vitro studies of the function of viral proteins, their interaction with each other and host proteins, new antivirals, and neutralizing antibodies in the context of the full viral life cycle. However, several challenges remain, including development of cell culture systems for all major HCV genotypes and identification of other susceptible cell lines.

Hepatitis C virus entry and neutralization

The processes of hepatitis C virus (HCV) entry and antibody-mediated neutralization are intimately linked. The high frequency of neutralizing antibodies (nAbs) that inhibit E2-CD81 interaction(s) suggests that this is a major target for the humoral immune response. The observation that HCV can transmit to naive cells by means of CD81-dependent and -independent routes in vitro awaits further investigation to assess the significance in vivo but may offer new strategies for HCV to escape nAbs. The identification of claudins in the entry process highlights the importance of cell polarity in defining routes of HCV entry and release, with recent experiments suggesting a polarized route of viral entry into cells in vitro. In this review, the authors summarize the current understanding of the mechanism(s) defining HCV entry and the role of nAbs in controlling HCV replication.