Interferon sensitivity-determining region of nonstructural region 5A of hepatitis C virus genotype 1b correlates with serum alanine aminotransferase levels in chronic infection

Response of hepatitis C virus to long-term passage in the presence of alpha interferon: multiple mutations and a common phenotype

Cell culture-produced hepatitis C virus (HCV) has been subjected to up to 100 serial passages in human hepatoma cells in the absence or presence of different doses of alpha interferon (IFN-α). Virus survival, genetic changes, fitness levels, and phenotypic traits have been examined. While high initial IFN-α doses (increasing from 1 to 4 IU/ml) did not allow HCV survival beyond passage 40, a gradual exposure (from 0.25 to 10 IU/ml) allowed the virus to survive for at least 100 passages. The virus passaged in the presence of IFN-α acquired IFN-α resistance as evidenced by enhanced progeny production and viral protein expression in an IFN-α environment. A partial IFN-α resistance was also noted in populations passaged in the absence of IFN-α. All lineages acquired adaptative mutations, and multiple, nonsynonymous mutations scattered throughout the genome were present in IFN-α-selected populations. Comparison of consensus sequences indicates a dominance of synonymous versus nonsynonymous substitutions. IFN-α-resistant populations displayed decreased sensitivity to a combination of IFN-α and ribavirin. A phenotypic trait common to all assayed viral populations is the ability to increase shutoff host cell protein synthesis, accentuated in infections with IFN-α-selected populations carried out in the presence of IFN-α. The trait was associated with enhanced phosphorylation of protein kinase R (PKR) and eIF2α, although other contributing factors are likely. The results suggest that multiple, independent mutational pathways can confer IFN-α resistance to HCV and might explain why no unified picture has been obtained regarding IFN-α resistance in vivo.

Disease progression in chronic hepatitis C: modifiable and nonmodifiable factors

The hepatic complications of chronic hepatitis C (CHC) usually occur only after progression to cirrhosis has taken place. Progression to cirrhosis, however, is extremely variable and depends on a broad set of host and viral factors that modify the rate at which fibrosis develops in a given individual. Despite their inherent limitations, studies of the natural history of CHC have identified several nonmodifiable factors associated with disease progression. These include age at acquisition of infection, sex, and race. More recent reports suggest important roles for host genetic polymorphisms and viral factors. Of greater immediate relevance to patients and their clinicians are the potentially modifiable factors, which include excessive alcohol consumption; smoking (tobacco and marijuana); insulin resistance; and coinfection with hepatitis B virus, human immunodeficiency virus type 1, or schistosomiasis. Unfortunately, to date, there are no reliable predictive models that can accurately estimate the risk of CHC disease progression.

Mutations in ISDR of NS5A gene influence interferon efficacy in Chinese patients with chronic hepatitis C virus genotype 1b infection

BACKGROUND AND AIM

The interferon sensitivity determining region (ISDR) in the non-structural 5A protein (NS5A) gene of hepatitis C virus genotype 1b (HCV-1b) has been demonstrated in Japanese patients; however, contradictory data have been reported from other parts of the world, particularly from Europe and the USA. This study investigated whether mutations in the ISDR of NS5A gene influence interferon efficacy in Chinese patients with chronic HCV-1b infection.

METHODS

Forty-five Chinese patients with chronic HCV infection were enrolled in a retrospective study. Of these patients, 20 with HCV-1b infection completed an interferon monotherapy course and 6-month follow-up. The pretreatment mutations in the nucleic acid sequence of NS5A 2209-2248 (ISDR) of HCV-1b were identified by sequencing RT-PCR products followed by comparison with the prototype sequence (HCV-J). Correlation with the clinical efficacy of interferon alpha therapy was then analyzed retrospectively.

RESULTS

The statistical analysis indicated a significant correlation between the mutations in ISDR of HCV-1b and sustained virological response to interferon alpha treatment (P < 0.05), and an association of the mutations in ISDR with the pretreatment serum alanine aminotransferase levels (P < 0.01) in Chinese patients with chronic HCV-1b infection.

CONCLUSIONS

The results support the concept that the response of HCV-1b infected patients towards interferon therapy is influenced by the mutations within the ISDR of NS5A gene.

[Effects of interferons on hepatitis C virus infection]

INTRODUCTION

The consequences of hepatitis C virus infections (chronic hepatitis, liver cirrhosis and hepatocellular carcinoma) are one of the major problems in clinical medicine. The persistence of infection in spite of high specific antibody titre suggests that the virus has the abillity to "escape" the immunological response.

INTERFERON THERAPY

Interferons are important components of the early host response to infection. They have antiviral, antiproliferative, and immunomodulatory activities. Many viruses have developed the ability to "annul" or alleviate the action of interferon by preventing its synthesis or by interfering with signaling pathways in the cells. During acute infection some of the non-structural proteins of HCV block regulatory factors that are responsible for the synthesis of endogenous infection. Within a cell, interferon induces a number of genes to produce proteins that prevent virus replication. Among them, the most important are RNA-dependent protein kinase and the eukaryotic initiation factor. However, viral proteins, especially viral envelope proteins and nonstructural protein 5A, prevent their phosphorylation and activation which enhance virus replication. These are the facts that have to be considered when using IFN in chronic hepatitis C patients.