Identification of the major, parenteral non-A, non-B hepatitis agent (hepatitis C virus) using a recombinant cDNA approach

Hemodialysis-Associated Infections

Hemodialysis patients are at increased risk of infections, which are common adverse events among this patient population. We review factors contributing to infections among hemodialysis patients and epidemiology of common infections and outbreaks, including bloodstream infections, vascular access infections, and infections caused by bloodborne pathogens. Recommendations for prevention are discussed with emphasis on essential infection control practices for hemodialysis settings.

Molecular characterization of HCV in a Swedish county over 8 years (2002-2009) reveals distinct transmission patterns

Background

Hepatitis C virus (HCV) is a major public health concern and data on its molecular epidemiology in Sweden is scarce. We carried out an 8-year population-based study of newly diagnosed HCV cases in one of Sweden's centrally situated counties, Södermanland (D-county). The aim was to characterize the HCV strains circulating, analyze their genetic relatedness to detect networks, and in combination with demographic data learn more about transmission.

Methods

Molecular analyses of serum samples from 91% (N=557) of all newly notified cases in D-county, 2002–2009, were performed. Phylogenetic analysis (NS5B gene, 300 bp) was linked to demographic data from the national surveillance database, SmiNet, to characterize D-county transmission clusters. The linear-by-linear association test (LBL) was used to analyze trends over time.

Results

The most prevalent subtypes were 1a (38%) and 3a (34%). Subtype 1a was most prevalent among cases transmitted via sexual contact, via contaminated blood, or blood products, while subtype 3a was most prevalent among people who inject drugs (PWIDs). Phylogenetic analysis revealed that the subtype 3a sequences formed more and larger transmission clusters (50% of the sequences clustered), while the 1a sequences formed smaller clusters (19% of the sequences clustered), possibly suggesting different epidemics.

Conclusion

We found different transmission patterns in D-county which may, from a public health perspective, have implications for how to control virus infections by targeted interventions.

Emerging and Reemerging Virus Diseases of Vertebrates☆

In the last two decades, a large number of new viruses have been discovered, many of which are pathogenic in humans or other vertebrates. Among the more important causes of virus emergence have been changes in human behavior, population, and increases in travel to distant countries. In addition, the application of new molecular technologies has led to the recognition of many viruses that hitherto went undetected. Many of the new, emerging viruses have an RNA genome, and many are zoonoses. The spread of human immunodeficiency virus, causing acquired immune deficiency syndrome, and the use of immunosuppressive drugs following transplant surgery, have increased the numbers of people in the population that are highly susceptible to emerging virus infections. The threat of a new pandemic of influenza virus in the human population stresses the need for development of better methods for detection, surveillance, and control of emerging virus diseases.

A cell-permeable peptide inhibits hepatitis C virus replication by sequestering IRES transacting factors

Hepatitis C virus (HCV) infection frequently leads to chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. There is no effective therapy or vaccine available to HCV-infected patients other than interferon-ribavarin combination, which is effective in a relatively small percentage of infected patients. Our previous results have shown that a synthetic peptide (LAP) corresponding to the N-terminal 18 amino acids of the Lupus autoantigen (La) was a potent inhibitor of HCV IRES-mediated translation. We demonstrate here that LAP efficiently blocks HCV replication of infectious JFH1 virus in cell culture. Our data suggest that LAP forms complexes with IRES-transacting factors (ITAFs) PTB and PCBP2. LAP-mediated inhibition of HCV IRES-mediated translation in vitro could be fully rescued by recombinant PCB and PCBP2. Also transient expression of PTB / PCBP2 combination significantly restores HCV replication in LAP-inhibited cultures. These results suggest that ITAFs could be potential targets to block HCV replication.

Emerging and Reemerging Virus Diseases of Vertebrates

In the last two decades, a large number of new viruses have been discovered, many of which are pathogenic in humans or other vertebrates. Among the more important causes of virus emergence have been changes in human behavior, population, and increases in travel to distant countries. In addition, the application of new molecular technologies has led to the recognition of many viruses that hitherto went undetected. Many of the new, emerging viruses have an RNA genome, and many are zoonoses. The spread of human immunodeficiency virus, causing acquired immune deficiency syndrome, and the use of immunosuppressive drugs following transplant surgery, have increased the numbers of people in the population that are highly susceptible to emerging virus infections. The threat of a new pandemic of influenza virus in the human population stresses the need for development of better methods for detection, surveillance, and control of emerging virus diseases.

A conserved basic loop in hepatitis C virus p7 protein is required for amantadine-sensitive ion channel activity in mammalian cells but is dispensable for localization to mitochondria

We previously identified the function of the hepatitis C virus (HCV) p7 protein as an ion channel in artificial lipid bilayers and demonstrated that this in vitro activity is inhibited by amantadine. Here we show that the ion channel activity of HCV p7 expressed in mammalian cells can substitute for that of influenza virus M2 in a cell-based assay. This was also the case for the p7 from the related virus, bovine viral diarrhoea virus (BVDV). Moreover, amantadine was shown to abrogate HCV p7 function in this assay at a concentration that specifically inhibits M2. Mutation of a conserved basic loop located between the two predicted trans-membrane alpha helices rendered HCV p7 non-functional as an ion channel. The intracellular localization of p7 was unaffected by this mutation and was found to overlap significantly with membranes associated with mitochondria. Demonstration of p7 ion channel activity in cellular membranes and its inhibition by amantadine affirm the protein as a target for future anti-viral chemotherapy.

Subversion of immune responses by hepatitis C virus: immunomodulatory strategies beyond evasion?

Hepatitis C virus (HCV) is an important human pathogen that causes mild to severe liver disease worldwide. This positive-strand RNA virus is remarkably efficient at establishing persistent infection. In order for a non-cytopathic virus such as HCV to persist, the virus must escape immune recognition or inhibit the host immune responses. Immune escape via mutations in antigenic sites may occur under selective pressure during B-cell or T-cell responses to HCV infection, and may serve as a mechanism for the establishment HCV persistence. In addition to antigenic variation, HCV is able to subvert the host immune response by encoding specific viral gene product(s). An understanding of the mechanisms behind HCV persistence will provide a basis for the rational design of vaccines and novel therapeutic agents targeting human HCV infection.

Managing occupational risks for hepatitis C transmission in the health care setting

Hepatitis C virus (HCV) infection is a significant contemporary health problem in the United States and elsewhere. Because it is primarily transmitted via blood, hepatitis C infection presents risks for both nosocomial transmission to patients and occupational spread to health care workers. Recent insights into the pathogenesis, immunopathogenesis, natural history, and treatment of infection caused by this unique flavivirus provide a rationale for the use of new strategies for managing occupational hepatitis C infections when they occur. This article reviews this developing information. Recently published data demonstrate success rates in the treatment of "acute hepatitis C syndrome" that approach 100\%, and although these studies are not directly applicable to all occupational infections, they may provide important clues to optimal management strategies. In addition, the article delineates approaches to the prevention of occupational exposures and also addresses the difficult issue of managing HCV-infected health care providers. The article summarizes currently available data about the nosocomial epidemiology of HCV infection and the magnitude of risk and discusses several alternatives for managing exposure and infection. No evidence supports the use of immediate postexposure prophylaxis with immunoglobulin, immunomodulators, or antiviral agents. Based on the very limited data available, the watchful waiting and preemptive therapy strategies described in detail in this article represent reasonable interim approaches to the complex problem of managing occupational HCV infections, at least until more definitive data are obtained.

The p7 protein of hepatitis C virus forms an ion channel that is blocked by the antiviral drug, Amantadine

Hepatitis C virus (HCV) cannot be grown in vitro, making biochemical identification of new drug targets especially important. HCV p7 is a small hydrophobic protein of unknown function, yet necessary for particle infectivity in related viruses [Harada, T. et al., (2000) J. Virol. 74, 9498-9506]. We show that p7 can be cross-linked in vivo as hexamers. Escherichia coli expressed p7 fusion proteins also form hexamers in vitro. These and HIS-tagged p7 function as calcium ion channels in black lipid membranes. This activity is abrogated by Amantadine, a compound that inhibits ion channels of influenza [Hay, A.J. et al. (1985) EMBO J. 4, 3021-3024; Duff, K.C. and Ashley, R.H. (1992) Virology 190, 485-489] and has recently been shown to be active in combination with current HCV therapies.

Endoplasmic reticulum (ER) stress: hepatitis C virus induces an ER-nucleus signal transduction pathway and activates NF-kappaB and STAT-3

Human hepatitis C virus (HCV) is the leading cause of chronic hepatitis, which often results in liver cirrhosis and hepatocellular carcinoma. The HCV RNA genome codes for at least ten proteins. The HCV non-structural protein 5A (NS5A) has generated considerable interest due to its effect on interferon sensitivity via binding and inactivating the cellular protein kinase, PKR. It has been shown that NS5A engages in the endoplasmic reticulum (ER)-nucleus signal transduction pathway. The expression of NS5A in the ER induces an ER stress ultimately leading to the activation of STAT-3 and NF-kappaB. This pathway is sensitive to inhibitors of Ca(2+) uptake in the mitochondria (ruthenium red), Ca(2+) chelators (TMB-8, EGTA-AM), and antioxidants (PDTC, NAC, Mn-SOD). The inhibitory effect of protein tyrosine kinase (PTK) inhibitors indicates the involvement of PTK in NF-kappaB activation by NS5A. This implicates an alternate pathway of NF-kappaB activation by NS5A. The actions of NS5A have also been studied in the context of an HCV subgenomic replicon inducing a similar intracellular event. Thus, activation of NF-kappaB leads to the induction of cellular genes, which are largely antiapoptotic in function. These studies suggest a potential function of NS5A in inducing chronic liver disease and hepatocellular carcinoma associated with HCV infection.

The outcome of hepatitis C virus infection is predicted by escape mutations in epitopes targeted by cytotoxic T lymphocytes

CD8(+) cytotoxic T lymphocytes (CTL) are thought to control hepatitis C virus (HCV) replication and so we investigated why this response fails in persistently infected individuals. The HCV quasispecies in three persistently infected chimpanzees acquired mutations in multiple epitopes that impaired class I MHC binding and/or CTL recognition. Most escape mutations appeared during acute infection and remained fixed in the quasispecies for years without further diversification. A statistically significant increase in the amino acid replacement rate was observed in epitopes versus adjacent regions of HCV proteins. In contrast, most epitopes were intact when hepatitis C resolved spontaneously. We conclude that CTL exert positive selection pressure against the HCV quasispecies and the outcome of infection is predicted by mutations in class I MHC restricted epitopes.

A small yeast RNA blocks hepatitis C virus internal ribosome entry site (HCV IRES)-mediated translation and inhibits replication of a chimeric poliovirus under translational control of the HCV IRES element

Hepatitis C virus (HCV) infection frequently leads to chronic hepatitis and cirrhosis of the liver and has been linked to development of hepatocellular carcinoma. We previously identified a small yeast RNA (IRNA) capable of specifically inhibiting poliovirus (PV) internal ribosome entry site (IRES)-mediated translation. Here we report that IRNA specifically inhibits HCV IRES-mediated translation both in vivo and in vitro. A number of human hepatoma (Huh-7) cell lines expressing IRNA were prepared and characterized. Constitutive expression of IRNA was not detrimental to cell growth. HCV IRES-mediated cap-independent translation was markedly inhibited in cells constitutively expressing IRNA compared to control hepatoma cells. However, cap-dependent translation was not significantly affected in these cell lines. Additionally, Huh-7 cells constitutively expressing IRNA became refractory to infection by a PV-HCV chimera in which the PV IRES is replaced by the HCV IRES. In contrast, replication of a PV-encephalomyocarditis virus (EMCV) chimera containing the EMCV IRES element was not affected significantly in the IRNA-producing cell line. Finally, the binding of the La autoantigen to the HCV IRES element was specifically and efficiently competed by IRNA. These results provide a basis for development of novel drugs effective against HCV infection.

Comparative features of hepatitis C virus infection in humans and chimpanzees

Several features of human HCV infection are recapitulated in the chimpanzee model. Most importantly, the frequency of persistent infection is high in both species, and virus replication occurs despite evidence of cellular and humoral immune responses. A key difference is that necroinflammatory lesions in chronically infected chimpanzees are almost always mild, whereas in humans the disease spectrum is very wide, ranging from mild to severe hepatitis and end-stage cirrhosis requiring transplantation. Understanding the basis for both the similarities and differences in persistent hepatitis C in the two species will probably be important for the development of effective prevention and therapy of HCV infection.

Sequence analysis of the hepatitis C virus (HCV) core gene suggests the core protein as an appropriate target for HCV vaccine strategies

Hepatitis C virus (HCV) is a major healthproblem with a prevalence of 1% in the United States population, and a significant percentage of infected patients progress to chronic liver disease and cirrhosis. Interferon therapy has demonstrated that the immune system can be modulated to alter the acute course of the disease, but long-term treatments remain elusive. Prevention of hepatitis C infection is therefore an important strategy to mitigate the impact of this disease. Initial attempts at vaccination have focused on recombinant envelope vaccines, which have shown an ability to protect against very low titre challenges of HCV in chimps. The need for vaccines capable of protecting against higher titre challenges has led to the search for alternative vaccine strategies. The most highly conserved structural protein in the HCV genome is the core protein, and vaccine strategies targeting the core protein have been proposed to increase vaccine efficacy. The variability of HCV core sequences and genotypes in the Ann Arbor patient population are not known, and the present study was undertaken to assess the theoretical feasibility of developing a HCV core vaccine by excluding promiscuous core (C) gene variability as a mechanism of vaccine failure. Results of nucleotide and deduced amino acid sequence analysis from 13 of 14 patients studied reveal a 93% nucleotide and 96.4% amino acid core sequence homology in the C gene regions studied. Genotype analysis revealed four of 14 to be type 1a and nine of 14 to be type 1b with one infection not being sufficiently characterized to determine genotype. These results demonstrate a sufficiently high degree of conservation of HCV core sequences in our patient population to permit design of a vaccine directed against core protein.

Identification and classification of viruses that have not been propagated

Microorganisms that cannot be grown in the laboratory can now be tentatively identified, by cloning and sequencing particular nucleic acid segments and then carrying out a comparative sequence analysis with an appropriate database. For bacteria, a few universally distributed genes and gene products have enabled comparative sequence analysis to be used for tentative identification and classification of uncultured bacteria. For viruses, there is no universally distributed viral gene or gene product. However, in a few cases, viruses that could not be propagated in the laboratory have been identified and classified. In these cases, either the entire viral genome sequence was determined or partial sequence information was supplemented with additional data. The Executive Committee of the International Committee on Taxonomy of Viruses (ICTV) has reviewed the issue of identification and classification of viruses that have not been propagated. Under the ICTV system, formal review of any taxonomic proposal is carried out by the relevant ICTV Subcommittee or Study Group. The few examples of unpropagated viruses that have arisen thus far have been readily accommodated within existing viral taxonomy, with the international group of experts comprising each Subcommittee and Study Group determining the necessary and sufficient amount of information needed for classification of an unpropagated virus on a case-by-case basis.

High efficiency prokaryotic expression and purification of a portion of the hepatitis C core protein and analysis of the immune response to recombinant protein in BALB/c mice

Hepatitis C virus (HCV) produces chronic persistent liver infection in 1-2% of the U.S. population and is the leading cause of end stage liver disease in patients presenting for liver transplantation at our center. Efforts to cure persistent HCV infection are frequently unsuccessful, so the development of a HCV vaccine is a high priority. HCV envelope proteins are hypervariable so production of a recombinant surface antigen vaccine such as is available for hepatitis B is not likely to confer widespread, high level protective immunity. As the most highly conserved structural protein in the HCV genome, the core protein is one reasonable target for vaccine production. Presented here are data on the manufacture of recombinant core protein containing partial carboxy terminus deletions in an effort to increase the efficiency of core expression. The maltose binding protein (MBP) and glutathione S-transferase (GST) protein prokaryotic expression systems were used to study two different constructs, expressing the first 140 and 163 amino acids of the core region. Deletion of the 23 amino acids (aa) from aa141-163 led to a marked increase in the efficiency of protein production from < 1 to 3-4 mg/liter for both systems studied. Protein purification was accomplished using affinity chromatography (MBP) or inclusion body isolation (GST) as determined by SDS-PAGE gels and immunotransblot with HCV core protein-specific monoclonal antibody. Finally, the immune response to recombinant protein was assessed in BALB/c mice using a MBP HCV core fusion protein and an ELISA developed using GST HCV core protein as a target. In all mice of this strain, serum anti-HCV core antibody titer increased to 10(-4), two logs above background, following immunization in conjunction with Freund's complete adjuvant. These results represent an encouraging first step toward production of a core protein vaccine. Recombinant core protein is a useful tool to study the immune response to core protein and may be useful to further study the epidemiology and biology of the HCV virus.

Molecular detection of hepatitis C virus: impact of detection methodology on clinical and laboratory correlations

The clinical manifestations of hepatitis C virus (HCV) infection are generally indistinguishable from other causes of viral hepatitis. HCV infections are usually anicteric, asymptomatic, and rarely cause acute fulminant liver failure. Serological testing for HCV in conjunction with epidemiological studies have verified that HCV was the major cause of parenterally transmitted non-A, non-B hepatitis (NANBH). With the widespread introduction of serological screening of blood products for HCV antibody, the risk of transfusion-associated HCV infection has been dramatically reduced (to < 3 cases per 10,000 units transfused). Despite the virtual elimination of transfusion-associated infections, the diagnosis of HCV remains important because > 50% of infections are sporadic in origin, 50 to 70% of infected individuals develop chronic hepatitis, and these individuals are at risk of developing cirrhosis (> 20%) as well as hepatocellular carcinoma. Although currently available anti-HCV immunoassays function well as blood-donor screening assays, they are poor at detecting acute infection because of the prolonged lag time between infection and detection of seroconversion (approximately 10 to 26 weeks for second-generation immunoassays). In contrast, polymerase chain reaction (PCR)-based detection of HCV RNA in serum can detect infection in as little as 1 to 2 weeks after exposure. This review focuses on the impact of modern serologic and nucleic acid-based HCV detection methodology on the clinical understanding of HCV infection, its associated illnesses, and its transmissability. Quantitative and reproducible nucleic acid-based detection assays will be required to provide additional insights into the clinical spectrum of HCV infections as well as to assess the efficacy of antiviral agents.

A conserved helical element is essential for internal initiation of translation of hepatitis C virus RNA

Translation of hepatitis C virus (HCV) RNA is initiated by cap-independent internal ribosome binding to the 5' noncoding region (NCR). To identify the sequences and structural elements within the 5' NCR of HCV RNA that contribute to the initiation of translation, a series of point mutations was introduced within this sequence. Since the pyrimidine-rich tract is considered a characteristic feature of picornavirus internal ribosome entry site (IRES) elements, our mutational analysis focused on two putative pyrimidine tracts (Py-I and Py-II) within the HCV 5' NCR. Translational efficiency of these mutant RNAs was examined by in vitro translation and after RNA transfection into liver-derived cells. Mutational analysis of Py-I (nucleotides 120 to 130), supported by compensatory mutants, demonstrates that the primary sequence of this motif is not important but that a helical structural element associated with this region is critical for HCV IRES function. Mutations in Py-II (nucleotides 191 to 199) show that this motif is dispensable for IRES function as well. Thus, the pyrimidine-rich tract motif, which is considered as an essential element of the picornavirus IRES elements, does not appear to be a functional component of the HCV IRES. Further, the insertional mutagenesis study suggests a requirement for proper spacing between the initiator AUG and the upstream structures of the HCV IRES element for internal initiation of translation.

Internal initiation of translation

Although the 5' cap-dependent scanning mechanism can account for the translational initiation of most mRNAs in eukaryotic cells, several viral and cellular mRNAs contain nucleotide sequences in their 5' non-coding regions that can mediate binding of ribosomes to the mRNA, regardless of the modification state of the 5' ends. During the past year, some nuclear proteins normally involved in RNA processing have been shown also to facilitate 'internal' ribosome binding. Unexpected dual functions have, therefore, been suggested for these RNA-binding proteins, in both RNA biogenesis in the nucleus and RNA translation in the cytoplasm.

Translation of human hepatitis C virus RNA in cultured cells is mediated by an internal ribosome-binding mechanism

The human hepatitis C virus (HCV) contains a long 5' noncoding region (5' NCR). Computer-assisted and biochemical analyses suggest that there is a complex secondary structure in this region that is comparable to the secondary structures that are found in picornaviruses (E.A. Brown, H. Zhang, L.-H. Ping, and S.M. Lemon, Nucleic Acids Res. 20:5041-5045, 1992). Previous in vitro studies suggest that the HCV 5' NCR plays an important role during translation (K. Tsukiyama-Kohara, N. Iizuka, M. Kohara, and A. Nomoto, J. Virol. 66:1476-1483, 1992). Dicistronic and monocistronic expression vectors, in vitro translation, RNA transfections, and deletion mutagenesis studies were utilized to demonstrate unambiguously that the HCV 5' NCR is involved in translational control. Our data strongly support the conclusion that an internal ribosome entry site exists within the 5' noncoding sequences proximal to the initiator AUG. Furthermore, our results suggest that the HCV genome is translated in a cap-independent manner and that the sequences immediately upstream of the initiator AUG are essential for internal ribosome entry site function during translation.