MicrobiologyBytes

When we think about virus pathogensis, we tend to get hung up on genetic variation and new “virulent” strains of virus appearing. The recent example of the Sydney 2012 strain of norovirus is a good example of this.

But we also know that around 20% of Europeans are highly resistant to symptomatic infections by noroviruses (Mendelian resistance to human norovirus infections. (2006) Seminars in immunology 18(6): 375-386).

Likewise, host variation in the IL28B gene is responsible for the outcome of hepatitis C virus (HCV) infection (Genetic Variation in the Interleukin-28B Gene Is Associated with Spontaneous Clearance and Progression of Hepatitis C Virus in Moroccan Patients. (2013) PLoS ONE 8(1): e54793).

So when you get sick, make sure you take your fair share of the responsibility!

216,000 people in the UK are now thought to be infected with hepatitis C virus (HCV) according to the UK Health Protection Agency (HPA). Thousands of people were also infected accidentally through contaminated blood products in the 1970s and 1980s. New diagnoses reported in England rose from 7,892 in 2010 to 9,908 in 2011. In the UK hospital admissions for end-stage liver disease related to hepatitis C rose from 612 in 1998 to 1,979 in 2010. Deaths rose from 98 in 1996 to 323 in 2010. The disease can take decades to manifest itself, although it is thought up to one in five people recover naturally in the first six months after contact. Symptoms include fatigue, weight loss, nausea, flu-like symptoms, problems concentrating, abdominal pain and jaundice.

HPA: Hepatitis C burden continues to grow. 26 July 2012

Currently, no vaccine exists for hepatitis C virus (HCV), a major pathogen thought to infect 170 million people globally. Many studies suggest that host T cell responses are critical for spontaneous resolution of disease, and preclinical studies have indicated a requirement for T cells in protection against challenge. Recent research aimed to elicit HCV-specific T cells with the potential for protection using a recombinant adenoviral vector strategy in a phase 1 study of healthy human volunteers.

Two adenovirus vectors expressing NS proteins from HCV genotype 1B were constructed based on rare serotypes [human adenovirus 6 (Ad6) and chimpanzee adenovirus 3 (ChAd3)]. Both vectors primed T cell responses against HCV proteins; these T cell responses targeted multiple proteins and were capable of recognizing heterologous strains (genotypes 1A and 3A). HCV-specific T cells consisted of both CD4+ and CD8+ T cell subsets; secreted interleukin-2, interferon-γ, and tumor necrosis factor–α; and could be sustained for at least a year after boosting with the heterologous adenoviral vector. Studies using major histocompatibility complex peptide tetramers revealed long-lived central and effector memory pools that retained polyfunctionality and proliferative capacity. These data indicate that an adenoviral vector strategy can induce sustained T cell responses of a magnitude and quality associated with protective immunity and open the way for studies of prophylactic and therapeutic vaccines for HCV.

Novel Adenovirus-Based Vaccines Induce Broad and Sustained T Cell Responses to HCV in Man. (2012) Science Translational Medicine 4(115), 115ra1

See also: NHS Choices – Experimental hepatitis C vaccine tested

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New research shows that Niemann-Pick C1–like 1 (NPC1L1) cholesterol uptake receptor is an HCV cell entry factor that functions after binding, at or before fusion. Together with the facts that NPC1L1 is a cellular cholesterol receptor, the HCV particle is enriched in cholesterol, and relative dependence on NPC1L1 is correlated with HCV particle cholesterol levels, supports and expands on previous reports suggesting that virion cholesterol is involved in HCV cell entry. Whether NPC1L1 directly interacts with HCV or indirectly participates in HCV entry by removing virion-associated cholesterol to perhaps reveal protected viral glycoprotein binding sites or confer a required conformational change remains to be determined. As NPC1L1 is expressed only on human and primate hepatocytes, this discovery additionally highlights NPC1L1 as a potential HCV tropism determinant, which may facilitate the future development of animal models of HCV infection.

Identification of the Niemann-Pick C1–like 1 cholesterol absorption receptor as a new hepatitis C virus entry factor. Nature Medicine 08 January 2012 doi:10.1038/nm.2581
Hepatitis C virus (HCV) is a leading cause of liver disease worldwide. With ~170 million individuals infected and current interferon-based treatment having toxic side effects and marginal efficacy, more effective antivirals are crucially needed. Although HCV protease inhibitors were just approved by the US Food and Drug Administration (FDA), optimal HCV therapy, analogous to HIV therapy, will probably require a combination of antivirals targeting multiple aspects of the viral lifecycle. Viral entry represents a potential multifaceted target for antiviral intervention; however, to date, FDA-approved inhibitors of HCV cell entry are unavailable. Here we show that the cellular Niemann-Pick C1–like 1 (NPC1L1) cholesterol uptake receptor is an HCV entry factor amendable to therapeutic intervention. Specifically, NPC1L1 expression is necessary for HCV infection, as silencing or antibody-mediated blocking of NPC1L1 impairs cell culture–derived HCV (HCVcc) infection initiation. In addition, the clinically available FDA-approved NPC1L1 antagonist ezetimibe potently blocks HCV uptake in vitro via a virion cholesterol–dependent step before virion-cell membrane fusion. Moreover, ezetimibe inhibits infection by all major HCV genotypes in vitro and in vivo delays the establishment of HCV genotype 1b infection in mice with human liver grafts. Thus, we have not only identified NPC1L1 as an HCV cell entry factor but also discovered a new antiviral target and potential therapeutic agent.

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Hepatocarcinogenesis (liver cancer) is, and will continue to be a major worldwide health problem. With chronic HBV and HCV infections being responsible for a significant proportion of HCC cases, the development of new and relevant cell culture and animal models to study the interactions of HBV and HCV with their host and the development of efficient means to combat chronic infections will remain major tasks to tackle. This publication gives an overview of our current state of knowledge in respect to the basic biology of these viruses, as well as the clinical and therapeutic options that have been, and are being developed, and highlights the major current technical and biological limitations that the field needs to overcome.

Hepatitis B and C Viruses and Hepatocellular Carcinoma. (2010) Viruses 2(8): 1504-1509 doi:10.3390/v2081504

Related:

• Hepatitis B virus integration and hepatocarcinogenesis
• The search for infectious causes of human cancers
• Liver flukes and cancer

In response to invasion with bacterial or viral pathogens, cells are able to mount an immediate immune response through their ability to use specialized cellular molecules, referred to as pattern recognition receptors or PRRs, to detect unusual DNA, ssRNA or dsRNA structures. This leads to induction of the interferons and pro-inflammatory cytokines that are involved in the innate immune response.

Hepatitis C virus (HCV) is one of the RNA helicase RIG-I-activating viruses, because of its 5′ppp-structured RNA, 3′-structured genomic RNA and replicative RNA duplexes. In contrast to other RIG-I activating viruses such as Sendai virus, influenza, or vesicular stomatitis virus, HCV is a poor inducer of IFN and pro-inflammatory cytokines in cell culture systems. One reason for this is that the HCV NS3/4A protease cleaves cellular proteins (MAVS), resulting in a rapid disruption of the IFN induction pathway.

A recent paper shows that HCV infection can stimulate the IFN induction pathway up to 12 hrs post-infection, whereas detection of MAVS cleavage begins at 18 hrs post-infection and is maximal at 24 hrs. The data reveal that 12 hrs post-infection, HCV promotes a rapid inhibition of IFN induction at the level of translation, indicating a new mechanism of regulation. This regulation was linked to activation of the dsRNA-activated eIF2α kinase PKR. Altogether, the results show that HCV uses PKR to control the translation of newly transcribed IFN mRNAs before sufficient NS3/4A protein can be synthesized to efficiently restrain transcription of IFN.

Although PKR is also recognized in several virus infections for its antiviral proprieties, it may be more suitable to control its action in the case of HCV infection. Therefore, a carefully-controlled use of PKR inhibitors, in conjunction with IFN/ribavirin, might be beneficial for the treatment of chronically HCV-infected patients, since it would lead to a boost in the induction of innate immunity and a sustained inhibition of the virus propagation.

Hepatitis C Virus Controls Interferon Production through PKR Activation. 2010 PLoS ONE 5(5): e10575. doi:10.1371/journal.pone.0010575

Related:

• Hepatitis C Virus: a mountain to climb
• The Interferon Antiviral Response
• Update on HBV and HCV Therapy

Lipid droplets consist of a core of neutral lipids surrounded by an outer phospholipid monolayer and associated proteins. These organelles are thought to be generated when neutral lipids accumulate in the endoplasmic reticulum (ER) bilayer. Recently, lipid droplets have been shown to play a role in several cellular processes, including lipid storage, lipid trafficking, and protein storage and degradation. The importance of this organelle is underscored by the fact that lipid droplets have been linked to several metabolic diseases, most notably diabetes and obesity. Lipid droplets have also been shown to play a critical role in the replication of several pathogens. One of the most well characterized examples is hepatitis C virus (HCV).

Viperin is an interferon (IFN)-induced antiviral protein that is induced upon HCV infection and inhibits HCV replication. Like the HCV NS proteins, viperin has been shown to localize to the cytosolic face of the ER through an N-terminal amphipathic
alpha-helix. This N-terminal amphipathic
alpha-helix is essential for viperin to inhibit HCV and influenza, as mutants lacking this domain have greatly reduced antiviral activity. Although the precise mechanism by which viperin inhibits HCV is still unknown, viperin was previously shown to inhibit influenza virus budding by disrupting plasma membrane lipid raft microdomains, which are sites of influenza virion assembly and budding. Independent of viral infection, the N-terminal amphipathic
alpha-helix of viperin inhibits protein secretion and appears to induce ER membrane curvature.

Numerous questions remain about how lipid droplets are generated and used by viruses. This paper shows that the IFN-induced antiviral protein viperin, which localizes to the cytosolic face of the ER and inhibits HCV, localizes to lipid droplets. This paper shows that the N-terminal amphipathic alpha-helix of viperin that is responsible for ER localization is also necessary and sufficient to localize both viperin and the fluorescent protein dsRed to lipid droplets. Point mutations in the alpha-helix that prevent ER association also disrupt lipid droplet association, and sequential deletion mutants indicate that the same number of helical turns are necessary for ER and lipid droplet association. The N-terminal amphipathic alpha-helix of the hepatitis C viral protein NS5A can localize dsRed and viperin to lipid droplets. These findings indicate that the amphipathic alpha-helices of viperin and NS5A are lipid droplet-targeting domains and suggest that viperin inhibits HCV by localizing to lipid droplets using a domain and mechanism similar to that used by HCV itself.

The antiviral protein, viperin, localizes to lipid droplets via its N-terminal amphipathic αalpha-helix. PNAS USA November 17 2009. doi: 10.1073/pnas.0911679106

Related:

• Viperin (cig5), an IFN-inducible antiviral protein directly induced by human cytomegalovirus. 2001 PNAS USA 98(26): 15125-15130
• Viroporins
• Hepatitis C Virus: a mountain to climb
• The Interferon Antiviral Response

Chronic hepatitis B virus (HBV) infection affects about 400 million people around the globe, being one of the most common infectious diseases and among the world’s leading causes of death. Antiviral therapy of chronic hepatitis B (CHB) aims to improve quality of life and survival chance of the patients by preventing progression of liver damage to cirrhosis, end-stage liver disease and liver cancer (HCC), thus preventing anticipated liver-related death. This goal is achieved by suppression of HBV replication in a sustained or maintained manner, either by short-term “curative” treatment with standard (IFN) and pegylated interferon (Peg-IFN) or long-term “suppressive” therapy with nucleos(t)ide analogues, like lamivudine, adefovir, entecavir, telbivudine and tenofovir. Since both strategies have advantages and disadvantages, the wise treatment of a patient with CHB requires careful balance between prediction of the natural history of HBV and of the potential benefit of anti- HBV therapy. Recent data on the long-term efficacy of third generation of nucleos(t)ide analogues entecavir and tenofovir have tipped the balance towards long-term suppression therapy as the first-line option for most patients with CHB, independent of the HBeAg status.

Chronic hepatitis C is a major worldwide health problem with an estimated prevalence of 1.6-2%. In Europe, more than 9 million chronic carriers and approximately 86,000 deaths per year are estimated due to the late complications of hepatitis C virus (HCV). The prognosis of chronic hepatitis C depends on the rate of fibrosis progression, which over a 20-30 year time span, may determine the risk of developing cirrhosis and its complications, namely HCC, liver decompensation, hepatic encephalopathy and oesophageal variceal bleeding. The only therapeutic intervention able to halt this progressive process is eradication of HCV by Interferon (IFN)-based therapies. Since the empirical choice to use IFN in 1986, therapy for chronic hepatitis C has constantly evolved over the past decade, with the attainable sustained virological response (SVR) rates increasing through the years. The addition of the guanosine nucleoside analogue ribavirin (Rbv) to IFN can be considered the major breakthrough in the treatment of chronic hepatitis C. Through mechanisms of action that still remain largely unknown, Rbv has determined a greater number of patients to ultimately achieve a SVR by increasing the rates of on-treatment response and reducing the rates of post-treatment relapse. In the large phase III clinical trials designed to assess its efficacy and safety, the combination of IFN and Rbv resulted in SVR rates of 30-35% in HCV genotype 1 patients and 75-80% in HCV-2 and 3 patients. These figures exceeded by far those obtained by IFN monotherapy, effectively leading the way for combination therapy to become the standard of care in the late 1990’s. The latest innovation in the treatment of chronic hepatitis C has been the pegylation of the IFN molecule (PegIFN) through the attachment of one or more polyethylene glycols to the IFN, a process that is able to modify the immunological, pharmacokinetic and pharmacodynamic properties of the drug. Standard IFN was in fact characterized by a number of limitations, such as poor stability, short elimination half-life and potential immunogenicity, that ultimately determined its small antiviral effect. Moreover, due to the increase in elimination half-life obtained by the pegylation process, it has been possible to lengthen the dosing interval from the unpractical three times a week schedule required by standard IFN, to the more “user friendly” once a week administration, a feature that has increased convenience whilst facilitating adherence to the recommended treatment schedule. Following the demonstration of a more potent antiviral effect in terms of SVR rates in phase III randomized trials, PegIFN has become the standard of care for chronic hepatitis C.

One year of interferon therapy inhibits HBV replication in one third of the patients whereas long-term administration of oral nucleos(t)ide analogues is efficient in most of them, as long as early treatment adaptation in patients with partial virological response and resistance is provided. Following the demonstration of a more potent antiviral effect in terms of sustained virological response (SVR) rates, Pegylated-IFN coupled with Ribavirin has become the standard treatment for chronic hepatitis C, with nearly 65% of all treated patients achieving a SVR. Long-term suppression of HBV and eradication of HCV would halt the progression of chronic hepatitis to cirrhosis, hepatocellular carcinoma and liver decompensation.

HBV and HCV Therapy. Viruses 2009, 1(3), 484-509. doi:10.3390/v1030484

Related:

• Hepatitis B and C viruses
• Hepatitis C Virus: a mountain to climb
• Does the outcome of HCV infection vary with the infecting virus type?
• Plugging the holes in hepatitis C virus antiviral therapy

http://www.nhs.uk/hepatitisc/Pages/default.aspx

Related:

• Hepatitis C Virus: a mountain to climb
• A breakthrough in understanding hepatitis C virus
• Does the outcome of HCV infection vary with the infecting virus type?
• Plugging the holes in hepatitis C virus antiviral therapy