Response to retreatment with interferon-alpha plus ribavirin in chronic hepatitis C patients is independent of the NS5A gene nucleotide sequence

Hepatitis C virus NS5A region mutation in chronic hepatitis C genotype 1 patients who are non-responders to two or more treatments and its relationship with response to a new treatment

AIM

To determine the number of mutations in the NS5A region of the hepatitis C virus (HCV) and its relationship to the response to antiviral therapy in patients with chronic hepatitis C genotype 1 who are non-responders to two or more treatments.

METHODS

Sequences within HCV NS5A [PKR binding domain (PKRBD) and the interferon-sensitivity-determining region (ISDR)] were analysed via direct sequencing in a selected cohort of 72 patients, with a total of 201 treatments [interferon-alpha (IFN-α), n = 49; IFN-α + ribavirin (RBV), n = 75; pegylated (peg) IFN-α + RBV, n = 47; first-generation direct-acting antivirals (DAAs), n = 13; and second-generation DAAs, n = 17]. Of these, 48/201 achieved a sustained virological response (SVR) and 153/201 achieved no virological response (NVR).

RESULTS

For both regions, treatments resulting in SVR were associated with more baseline mutations than were treatments resulting in NVR (SVR vs NVR; PKRBD: 5.82 ± 3 vs 4.86 ± 2 mutations, P = 0.045; ISDR: 2.65 ± 2 vs 1.51 ± 1.7 mutations, P = 0.005). A decrease or no change in the number of mutations over time between treatments in the PKRBD or ISDR, as shown by sequencing, was associated with patients who usually failed to respond to treatment (PKRBD, P = 0.02; ISDR, P = 0.001). Moreover, patients showing a post-treatment baseline viral load > 600000 IU/mL and increased ISDR mutations with respect to the previous treatment were 9.21 times more likely to achieve SVR (P = 0.001).

CONCLUSION

The obtained results show that among patients who have shown no response to two or more antiviral treatments, the likelihood of achieving SVR increases with the genetic variability in the ISDR region (≥ 2 mutations or number of substitutions from the HCV-J and HCV-1 prototype), especially when the viral load is greater than 600000 IU/mL.

RNA structural elements of hepatitis C virus controlling viral RNA translation and the implications for viral pathogenesis

Hepatitis C virus (HCV) genome multiplication requires the concerted action of the viral RNA, host factors and viral proteins. Recent studies have provided information about the requirement of specific viral RNA motifs that play an active role in the viral life cycle. RNA regulatory motifs controlling translation and replication of the viral RNA are mostly found at the 5' and 3' untranslated regions (UTRs). In particular, viral protein synthesis is under the control of the internal ribosome entry site (IRES) element, a complex RNA structure located at the 5'UTR that recruits the ribosomal subunits to the initiator codon. Accordingly, interfering with this RNA structural motif causes the abrogation of the viral cycle. In addition, RNA translation initiation is modulated by cellular factors, including miRNAs and RNA-binding proteins. Interestingly, a RNA structural motif located at the 3'end controls viral replication and establishes long-range RNA-RNA interactions with the 5'UTR, generating functional bridges between both ends on the viral genome. In this article, we review recent advances on virus-host interaction and translation control modulating viral gene expression in infected cells.

Evidence of recombination in intrapatient populations of hepatitis C virus

Hepatitis C virus (HCV) is a major cause of liver disease worldwide and a potential cause of substantial morbidity and mortality in the future. HCV is characterized by a high level of genetic heterogeneity. Although homologous recombination has been demonstrated in many members of the family Flaviviridae, to which HCV belongs, there are only a few studies reporting recombination on natural populations of HCV, suggesting that these events are rare in vivo. Furthermore, these few studies have focused on recombination between different HCV genotypes/subtypes but there are no reports on the extent of intra-genotype or intra-subtype recombination between viral strains infecting the same patient. Given the important implications of recombination for RNA virus evolution, our aim in this study has been to assess the existence and eventually the frequency of intragenic recombination on HCV. For this, we retrospectively have analyzed two regions of the HCV genome (NS5A and E1-E2) in samples from two different groups: (i) patients infected only with HCV (either treated with interferon plus ribavirin or treatment naïve), and (ii) HCV-HIV co-infected patients (with and without treatment against HIV). The complete data set comprised 17712 sequences from 136 serum samples derived from 111 patients. Recombination analyses were performed using 6 different methods implemented in the program RDP3. Recombination events were considered when detected by at least 3 of the 6 methods used and were identified in 10.7% of the amplified samples, distributed throughout all the groups described and the two genomic regions studied. The resulting recombination events were further verified by detailed phylogenetic analyses. The complete experimental procedure was applied to an artificial mixture of relatively closely viral populations and the ensuing analyses failed to reveal artifactual recombination. From these results we conclude that recombination should be considered as a potentially relevant mechanism generating genetic variation in HCV and with important implications for the treatment of this infection.

Relevance of RNA structure for the activity of picornavirus IRES elements

The RNA of all members of the Picornaviridae family initiates translation internally, via an internal ribosome entry site (IRES) element present in their 5' untranslated region. IRES elements consist of cis-acting RNA structures that often operate in association with specific RNA-binding proteins to recruit the translational machinery. This specialized mechanism of translation initiation is shared with other viral RNAs, and represents an alternative to the general cap-dependent initiation mechanism. In this review we discuss recent evidences concerning the relationship between RNA structure and IRES function in the genome of picornaviruses. The biological implications of conserved RNA structural elements for the mechanism of internal translation initiation driven by representative members of enterovirus and rhinovirus (type I IRES) and cardiovirus and aphthovirus (type II IRES) will be discussed.

Hepatitis C virus and the controversial role of the interferon sensitivity determining region in the response to interferon treatment

The degree of variability of the interferon sensitivity determining region (ISDR) in the hepatitis C virus (HCV) genome has been postulated to predict the response to interferon therapy, mainly in patients infected with subtype 1b, although this prediction has been the subject of a long controversy. This prediction has been tested by analyzing a cohort of 67 Spanish patients infected with HCV genotype 1, 23 of which were infected with subtype 1a and 44 with subtype 1b. A sample previous to therapy with alpha-interferon plus ribavirin was obtained and several clones (between 25 and 96) including the ISDR were sequenced from each patient. A significant correlation between mutations at the ISDR and response to treatment for subtype 1b patients, but not for those infected with subtype 1a, has been detected. Although the results suggest that the same relationship holds true for subtype 1a, lack of statistical power because of the small sample size of this subtype prevented firmer conclusions. However, identical ISDR sequences were found in responder and non-responder patients, suggesting that the stability of the ISDR sequence can occasionally help HCV to evade interferon therapy, although this is not a sufficient condition. More complex interactions, including the ISDR or not, are likely to exist and govern the HCV response to interferon treatment.

Drug resistance in antiviral treatment for infections with hepatitis B and C viruses

Treatments for infections with hepatitis B and C viruses have recently developed markedly, and range from nonspecific interferon-based treatments to specific antiviral treatments, such as those that inhibit hepatitis virus-coded protein production or activity. These developments have contributed to the achievement of excellent enhancement of the antiviral effect. On the other hand, the development of specific antiviral therapies has created unprecedented problems. Antiviral drug-resistant strains of viruses have emerged, leading to a poor prognosis for infected patients. Clarification of the mechanisms underlying the emergence of such resistance to drugs will be useful for the treatment of such patients. In this review, we outline pathological conditions associated with hepatitis B and C viruses and their treatments, and discuss the current situation and mechanisms underlying the emergence of antiviral drug-resistant strains.

Correlation of amino acid variations within nonstructural 4B protein with initial viral kinetics during interferon-alpha-based therapy in HCV-1b-infected patients

Chronic hepatitis C is a major cause of liver cirrhosis leading to chronic liver failure and hepatocellular carcinoma. Different hepatitis C virus (HCV) proteins have been associated with resistance to interferon-alpha-based therapy. However, the exact mechanisms of virus-mediated interferon resistance are not completely understood. The importance of amino acid (aa) variations within the HCV nonstructural (NS)4B protein for replication efficiency and viral decline during the therapy is unknown. We investigated pretreatment sera from 42 patients with known outcome to interferon-based therapy. The complete NS4B gene was amplified and sequenced. Mutational analyses of predicted conformational, functional, structural and phylogenetic properties of the deduced aa sequences were performed. The complete NS4B protein was highly conserved with a median frequency of 0.015 +/- 0.009 aa exchanges (median +/- SD, 4.00 +/- 2.31). Especially within the predicted transmembranous domains of the NS4B protein, the mean number of aa variations was low (median frequency, 0.013 +/- 0.013). Neither the number of aa variations nor specific aa exchanges were correlated with HCV RNA serum concentration at baseline. A rapid initial HCV RNA decline of >/=1.5 log(10) IU/mL at week 2 of interferon-based therapy was associated with a higher frequency of nonconservative aa exchanges within the complete NS4B protein in comparison with patients with a nonrapid HCV RNA decline (median frequency, 0.011 +/- 0.005 vs 0.004 +/- 0.003, P = 0.006). Overall, the aa sequence of the NS4B protein was highly conserved, indicating an important role for replication in vivo. Amino acid variations with relevant changes of physicochemical properties may influence replication efficiency, associated with a rapid early virological response.

A mutation in the interferon sensitivity-determining region is associated with responsiveness to interferon-ribavirin combination therapy in chronic hepatitis patients infected with a Japan-specific subtype of hepatitis C virus genotype 1B

The interferon sensitivity-determining region (ISDR) is useful as a predictive marker of the response to interferon (IFN) therapy for chronic hepatitis patients with a Japan-specific subtype (J-type) of hepatitis C virus (HCV) genotype 1b. This marker is not useful for predicting responsiveness of a worldwide subtype (W-type) of HCV 1b, which could explain the restricted usefulness of this system only to Japan. In the present study, we examined the predictive value of the ISDR for ribavirin combination therapy. A total of 79 patients with HCV 1b comprising 35 patients with J-type and 44 patients with W-type were treated with IFN in combination with ribavirin for more than 48 weeks. Mutations in the ISDR were detected more frequently often seen in J-type HCV 1b than in W-type; however, the sustained virological response (SVR) rate for the combination therapy was similar between the two subtypes. Multivariate analysis revealed that factors associated with SVR were IFN dose and the number of amino acid substitutions in ISDR but not with subtypes J and W. The correlation between the number of substitutions in ISDR and responses to IFN-ribavirin combination therapy was restricted to patients with J-type HCV 1b. The ISDR is a useful predictive marker for response to IFN-ribavirin combination therapy in J-type HCV.

Molecular biology and clinical implication of hepatitis C virus

Hepatitis C virus (HCV) was first described in 1989 as the putative viral agent of non-A non-B hepatitis. It is a member of the Flaviviridae family and has been recognized as the major causative agent of chronic liver disease, including chronic active hepatitis, cirrhosis and hepatocellular carcinoma. HCV is a positive RNA virus with a genome containing approximately 9500 nucleotides. It has an open reading frame that encodes a large polyprotein of about 3000 amino acids and is characterized by extensive genetic diversity. HCV has been classified into at least 6 major genotypes with many subtypes and circulates within an infected individual as a number of closely related but distinct variants known as quasispecies. This article reviews aspects of the molecular biology of HCV and their clinical implication.

Meta-Analysis of Mutations in the Ns5A Gene and Hepatitis C Virus Resistance to Interferon Therapy: Uniting Discordant Conclusions

Background

Hepatitis C virus genotype 1B responds poorly to treatment with interferon, in contrast to the more interferon-sensitive genotypes 2 and 3. Studies on combination therapy regimens with PEG-interferon and ribavirin report sustained response rates that generally do not exceed 50%, in contrast to sustained response rates of 80% for genotype 2 and 3. In Japan, a correlation was found between the number of mutations in an ‘interferon sensitivity determining region’ (ISDR) and outcome of interferon treatment in genotype 1B-infected patients. However, an ongoing controversy on the existence of an ISDR in non-Japanese isolates resulted, as non-Japanese studies failed to confirm this association. The present study approached this issue by carrying out a meta-analysis of ISDR sequences and response to interferon treatment.

Methods

Twenty-seven studies were included, reporting 1351 ISDR sequence data of genotype 1B-infected patients and their virological response to interferon treatment. Both summary statistics and individual patient data were used systematically to explore the association between ISDR mutations and response to interferon.

Results

The ISDR effect on response was universally present but appeared to be stronger in Japan, with a relative risk of 5.73 for mutant viruses as compared to 4.66 for non-Japanese isolates. High interferon dose, in Japan administered more frequently, was associated with an increase in response rate only among patients infected with mutant isolates. Interaction between dose and ISDR type was confirmed in a logistic regression model. After stratifying for dose, differences in response rate between Japanese and non-Japanese patients were no longer present.

Conclusion

This study puts an end to a longstanding controversy by confirming the universal existence of an ISDR in genotype 1B-infected patients. Apparent discrepant findings from Japanese and non-Japanese studies can be explained by differences in dosing regimens and a dose-dependent differential effect of ISDR mutations on response to treatment.

Constitutive over-expression of the insulin receptor substrate-1 causes functional up-regulation of Fas receptor

BACKGROUND/AIMS

Insulin- and insulin growth factor-1 stimulated signaling through the insulin receptor substrate-1 (IRS-1) promotes hepatocellular proliferation and survival. IRS-1 over-expression in transgenic (Tg) mouse livers caused constitutive activation of Erk mitogen activated protein kinase (MAPK) and phosphatidylinositol-3 kinase (PI3K) resulting in significantly increased levels of DNA synthesis and larger hepatic masses relative to non-transgenic (non-Tg) littermates. However, the livers eventually ceased to grow but remained approximately 25% larger than non-Tg livers. We hypothesized that this growth homeostasis was achieved by parallel activation of pro-apoptosis pathways.

METHODS

Since Fas-mediated apoptosis is a common mechanism of hepatocyte destruction, we investigated the potential role of Fas receptor as a regulator of hepatic mass in IRS-1 transgenic mice.

RESULTS

Significantly increased Fas-receptor levels were detected in the livers of IRS-1 Tg compared to non-Tg mice by Western blot analysis. Functional activation of Fas-receptor in IRS-1 Tg livers was demonstrated by increased hepatocellular apoptosis caused by intravenous injection of anti-Fas (Jo-2).

CONCLUSIONS

These findings suggest that the increased growth caused by IRS-1 over-expression is balanced by constitutive activation of pro-death mechanisms. Failure of the IRS-1 Tg mice to develop liver cancer may be due to preservation of pro-growth, pro-death homeostasis mechanisms.

Diagnosed with Hepatitis C: a descriptive exploratory study

A descriptive exploratory study was carried out to elicit the felt-experience of Hepatitis C infection. A non-probability sampling strategy was employed which generated a sample of nine participants for in-depth interview. Data analysis revealed that the diagnosis had precipitated a transition in the participants' lives. Factors were identified that served as barriers and facilitators to their transition experience. At the time of data collection all of the participants were not experiencing indicators of a healthy transition. It was evident that the transitional experience was neither time-bound nor linear in nature.

Hepatitis C virus and its pathogenesis

Hepatitis C virus is a major causative agent of chronic hepatitis and the development of hepatocellular carcinoma. However, the roles of this virus in these diseases remain to be clarified, although it is likely that cytotoxic T lymphocytes (CTL) play crucial roles in the clearance of virus-infected cells, thus causing inflammation. In many, cases the clearance is not sufficient to eradicate all infected cells. This may be due to insufficient activation of CTL. In addition, it is also likely that the virus has some mechanism to escape from clearance. One such mechanism may be the suppression of apoptosis by activation of NF-kB or mitogenic function by virus proteins, and these functions may also be linked to the development of hepatocellular carcinoma.