The green tea polyphenol, epigallocatechin-3-gallate, inhibits hepatitis C virus entry

Hepatitis C virus (HCV) is a major cause of liver cirrhosis and hepatocellular carcinoma. Current antiviral therapy fails to clear infection in a substantial proportion of cases. Drug development is focused on nonstructural proteins required for RNA replication. Individuals undergoing orthotopic liver transplantation face rapid, universal reinfection of the graft. Therefore, antiviral strategies targeting the early stages of infection are urgently needed for the prevention of HCV infection. In this study, we identified the polyphenol, epigallocatechin-3-gallate (EGCG), as an inhibitor of HCV entry. Green tea catechins, such as EGCG and its derivatives, epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC), have been previously found to exert antiviral and antioncogenic properties. EGCG had no effect on HCV RNA replication, assembly, or release of progeny virions. However, it potently inhibited Cell-culture-derived HCV (HCVcc) entry into hepatoma cell lines as well as primary human hepatocytes. The effect was independent of the HCV genotype, and both infection of cells by extracellular virions and cell-to-cell spread were blocked. Pretreatment of cells with EGCG before HCV inoculation did not reduce HCV infection, whereas the application of EGCG during inoculation strongly inhibited HCV infectivity. Moreover, treatment with EGCG directly during inoculation strongly inhibited HCV infectivity. Expression levels of all known HCV (co-)receptors were unaltered by EGCG. Finally, we showed that EGCG inhibits viral attachment to the cell, thus disrupting the initial step of HCV cell entry. Conclusion: The green tea molecule, EGCG, potently inhibits HCV entry and could be part of an antiviral strategy aimed at the prevention of HCV reinfection after liver transplantation.     

Serum amyloid A has antiviral activity against hepatitis C virus by inhibiting virus entry in a cell culture system

Serum amyloid A (SAA) is an acute phase protein produced by the liver. SAA concentration increases markedly in the serum following inflammation and infection. Large increases in SAA concentration during the acute phase response suggest that SAA has a beneficial role in host defense. This study sought to determine the effect of SAA on hepatitis C virus (HCV) infectivity using retroviral particles pseudotyped with HCV envelope glycoproteins (HCVpp) and the recently developed cell culture system for HCV (HCVcc). SAA inhibited HCVpp and HCVcc infection in a dose-dependent manner by affecting an early step of the virus life cycle. Further characterization with HCVpp indicated that SAA blocks virus entry by interacting with the viral particle. In addition, the antiviral activity of SAA was strongly reduced when high-density lipoproteins (HDL) were coincubated with SAA. However, HDL had only a slight effect on the antiviral activity of SAA when HCVpp was first preincubated with SAA. Furthermore, analyses of SAA in sera of chronic HCV patients revealed the presence of variable levels of SAA with abnormally elevated concentrations in some cases. However, no obvious clinical correlation was found between SAA levels and HCV viral loads. In conclusion, our data demonstrate an antiviral activity for SAA and suggest a tight relationship between SAA and HDL in modulating HCV infectivity.     

Chronic hepatitis C virus infection and lipoprotein metabolism

Hepatitis C virus (HCV) is a hepatotrophic virus and a major cause of chronic liver disease, including hepatocellular carcinoma, worldwide. The life cycle of HCV is closely associated with the metabolism of lipids and lipoproteins. The main function of lipoproteins is transporting lipids throughout the body. Triglycerides, free cholesterol, cholesteryl esters, and phospholipids are the major components of the transported lipids. The pathway of HCV assembly and secretion is closely linked to lipoprotein production and secretion, and the infectivity of HCV particles largely depends on the interaction of lipoproteins. Moreover, HCV entry into hepatocytes is strongly influenced by lipoproteins. The key lipoprotein molecules mediating these interactions are apolipoproteins. Apolipoproteins are amphipathic proteins on the surface of a lipoprotein particle, which help stabilize lipoprotein structure. They perform a key role in lipoprotein metabolism by serving as receptor ligands, enzyme co-factors, and lipid transport carriers. Understanding the association between the life cycle of HCV and lipoprotein metabolism is important because each step of the life cycle of HCV that is associated with lipoprotein metabolism is a potential target for anti-HCV therapy. In this article, we first concisely review the nature of lipoprotein and its metabolism to better understand the complicated interaction of HCV with lipoprotein. Then, we review the outline of the processes of HCV assembly, secretion, and entry into hepatocytes, focusing on the association with lipoproteins. Finally, we discuss the clinical aspects of disturbed lipid/lipoprotein metabolism and the significance of dyslipoproteinemia in chronic HCV infection with regard to abnormal apolipoproteins.     

Impact of lipids and lipoproteins on hepatitis C virus infection and virus neutralization

Hepatitis C virus(HCV)infections represent a major global health problem.End-stage liver disease caused by chronic HCV infection is a major indication for liver transplantation.However,after transplantation the engrafted liver inevitably becomes infected by the circulating virus.Direct acting antivirals are not yet approved for use in liver transplant patients,and limited efficacy and severe side effects hamper the use of pegylated interferon combined with ribavirin in a post-transplant setting.Therefore,alternative therapeutic options need to be explored.Viral entry represents an attractive target for such therapeutic intervention.Understanding the mechanisms of viral entry is essential to define the viral and cellular factors involved.The HCV life cycle is dependent of and associated with lipoprotein physiology and the presence of lipoproteins has been correlated with altered antiviral efficacy of entry inhibitors.In thisreview,we summarise the current knowledge on how lipoprotein physiology influences the HCV life cycle.We focus especially on the influence of lipoproteins on antibodies that target HCV envelope proteins or antibodies that target the cellular receptors of the virus.This information can be particularly relevant for the prevention of HCV re-infection after liver transplantation.     

A human claudin-1-derived peptide inhibits hepatitis C virus entry

Hepatitis C virus (HCV) entry is a complicated process that requires multiple host factors, such as CD81, scavenger receptor BI, claudin-1 (CLDN1), and occludin. The interaction of virus and cellular entry factors represents a promising target for novel anti-HCV drug development. In this study, we sought to identify peptide inhibitors for HCV entry by screening a library of overlapping peptides covering the four above-mentioned entry factors. An 18-amino acid peptide (designated as CL58) that was derived from the CLDN1 intracellular and first transmembrane region inhibited both de novo and established HCV infection in vitro. Unlike previously reported peptides corresponding to CLDN1 extracellular loops, CL58 did not alter the normal distribution of CLDN1 and was not cytotoxic in vitro at concentrations nearly 100-fold higher than the effective antiviral dose. The inhibitory effect of CL58 appeared to occur at a late step during viral entry, presumably after initial binding. Finally, overexpressed CL58 was able to interact with HCV envelope proteins. CONCLUSION: We identified a novel CLDN1-derived peptide that inhibits HCV entry at a postbinding step. The findings expand our knowledge of the roles that CLDN1 play in HCV entry and highlight the potential for developing a new class of inhibitors targeting the viral entry process.     

The hepatitis C virus life cycle as a target for new antiviral therapies

The burden of disease consequent to hepatitis C virus (HCV) infection has been well described and is expected to increase dramatically over the next decade. Current approved antiviral therapies are effective in eradicating the virus in approximately 50% of infected patients. However, pegylated interferon and ribavirin-based therapy is costly, prolonged, associated with significant adverse effects, and not deemed suitable for many HCV-infected patients. As such, there is a clear and pressing need for the development of additional agents that act through alternate or different mechanisms, in the hope that such regimens could lead to enhanced response rates more broadly applicable to patients with hepatitis C infection. Recent basic science enhancements in HCV cell culture systems and replication assays have led to a broadening of our understanding of many of the mechanisms of HCV replication and, therefore, potential novel antiviral targets. In this article, we have attempted to highlight important new information as it relates to our understanding of the HCV life cycle. These steps broadly encompass viral attachment, entry, and fusion; viral RNA translation; posttranslational processing; HCV replication; and viral assembly and release. In each of these areas, we present up-to-date knowledge of the relevant aspects of that component of the viral life cycle and then describe the preclinical and clinical development targets and pathways being explored in the translational and clinical settings.     

Hepatitis C virus entry: molecular biology and clinical implications

With an estimated 170 million infected individuals, hepatitis C virus (HCV) has a major impact on public health. A vaccine protecting against HCV infection is not available, and current antiviral therapies are characterized by limited efficacy, high costs, and substantial side effects. Binding of the virus to the cell surface followed by viral entry is the first step in a cascade of interactions between virus and the target cell that is required for the initiation of infection. Because this step represents a critical determinant of tissue tropism and pathogenesis, it is a major target for host cell responses such as antibody-mediated virus-neutralization-and a promising target for new antiviral therapy. The recent development of novel tissue culture model systems for the study of the first steps of HCV infection has allowed rapid progress in the understanding of the molecular mechanisms of HCV binding and entry. This review summarizes the impact of recently identified viral and host cell factors for HCV attachment and entry. Clinical implications of this important process for the pathogenesis of HCV infection and novel therapeutic interventions are discussed.     

Targeting host factors： A novel rationale for the management of hepatitis C virus

Hepatitis C is recognized as a major threat to global public health. The current treatment of patients with chronic hepatitis C is the addition of ribavirin to interferon-based therapy which has limited efficacy, poor tolerability, and significant expense. New treatment options that are more potent and less toxic are much needed. Moreover, more effective treatment is an urgent priority for those who relapse or do not respond to current regimens. A major obstacle in combating hepatitis C virus （HCV） infection is that the fidelity of the viral replication machinery is notoriously low, thus enabling the virus to quickly develop mutations that resist compounds targeting viral enzymes. Therefore, an approach targeting the host cofactors, which are indispensable for the propagation of viruses, may be an ideal target for the development of antiviral agents because they have a lower rate of mutation than that of the viral genome, as long as they have no side effects to patients. Drugs targeting, for example, receptors of viral entry, host metabolism or nuclear receptors, which are factors required to complete the HCV life cycle, may be more effective in combating the viral infection. Targeting host cofactors of the HCV life cycle is an attractive concept because it imposes a higher genetic barrier for resistance than direct antiviral compounds. However the principle drawback of this strategy is the greater potential for cellular toxicity.     

Hepatitis C virus entry into hepatocytes: molecular mechanisms and targets for antiviral therapies

Hepatitis C virus (HCV) is a major cause of liver cirrhosis and hepatocellular carcinoma. Preventive modalities are absent and the current antiviral treatment is limited by resistance, toxicity, and high costs. Viral entry is required for initiation, spread, and maintenance of infection, and thus is a promising target for antiviral therapy. HCV entry is a highly orchestrated process involving viral and host cell factors. These include the viral envelope glycoproteins E1 and E2, CD81, scavenger receptor BI, and tight junction proteins claudin-1 and occludin. Recent studies in preclinical models and HCV-infected patients have demonstrated that the virus has developed multiple strategies to escape host immune responses during viral entry. These include evasion from neutralizing antibodies and viral spread by cell-cell transmission. These challenges have to be taken into account for the design of efficient antiviral strategies. Thus, a detailed understanding of the mechanisms of viral entry and escape is a prerequisite to define viral and cellular targets and develop novel preventive and therapeutic antivirals. This review summarizes the current knowledge about the molecular mechanisms of HCV entry into hepatocytes, highlights novel targets and reviews the current preclinical and clinical development of compounds targeting entry. Proof-of-concept studies suggest that HCV entry inhibitors are a novel and promising class of antivirals widening the preventive and therapeutic arsenal against HCV infection.     

A cell-based, high-throughput screen for small molecule regulators of hepatitis C virus replication

BACKGROUND & AIMS: Only half of patients with chronic hepatitis C virus (HCV) infection experience sustained virologic response to pegylated-interferon and ribavirin, which cause numerous side effects. Thus, the identification of more effective and better tolerated agents is a high priority. We applied chemical biology to screen small molecules that regulate HCV. METHODS: We first optimized the Huh7/Rep-Feo replicon cell line for the 384-well microplate format and used this line to screen a large library of well-characterized, known biologically active compounds using automated technology. After identifying several molecules capable of either stimulating or inhibiting HCV replication in this primary screen, we then validated our hit compounds using a full-length HCV replicon cell line in secondary screens. RESULTS: We identified and validated a number of antiviral and proviral agents, including HMG-CoA reductase inhibitors (antiviral) and corticosteroids (proviral). The finding of increased replication associated with corticosteroids suggests that these agents directly promote viral replication independent of their suppressive effects on the immune response. The finding of antiviral activity associated with the HMG-CoA reductase inhibitors implies an important role for lipid metabolism in the viral life cycle. CONCLUSIONS: We have developed a simple, reproducible, and reliable cell-based high-throughput screening assay system using an HCV replicon model to identify small molecules that regulate HCV replication. This method can be used to identify not only putative antiviral agents, but also cellular regulators of viral replication.     

Last stop before exit - hepatitis C assembly and release as antiviral drug targets

Chronic Hepatitis C infection is a global health problem. While primary infection is often inapparent, it becomes chronic in most cases. Chronic infection with Hepatitis C virus (HCV) frequently leads to liver cirrhosis or liver cancer. Consequently, HCV infection is one of the leading causes for liver transplantation in industrialized countries. Current treatment is not HCV specific and is only effective in about half of the infected patients. This situation underlines the need for new antivirals against HCV. To develop new and more efficient drugs, it is essential to specifically target the different steps of the viral life cycle. Of those steps, the targeting of HCV assembly has the potential to abolish virus production. This review summarizes the advances in our understanding of HCV particle assembly and the identification of new antiviral targets of potential interest in this late step of the HCV life cycle.     

A virocidal amphipathic {alpha}-helical peptide that inhibits hepatitis C virus infection in vitro

An amphipathic alpha-helical peptide (C5A) derived from the membrane anchor domain of the hepatitis C virus (HCV) NS5A protein is virocidal for HCV at submicromolar concentrations in vitro. C5A prevents de novo HCV infection and suppresses ongoing infection by inactivating both extra- and intracellular infectious particles, and it is nontoxic in vitro and in vivo at doses at least 100-fold higher than required for antiviral activity. Mutational analysis indicates that C5A's amphipathic alpha-helical structure is necessary but not sufficient for its virocidal activity, which depends on its amino acid composition but not its primary sequence or chirality. In addition to HCV, C5A inhibits infection by selected flaviviruses, paramyxoviruses, and HIV. These results suggest a model in which C5A destabilizes viral membranes based on their lipid composition, offering a unique therapeutic approach to HCV and other viral infections.     

Modulation of host lipid metabolism by hepatitis C virus: role of new therapies

It is well established that hepatitis C virus(HCV) infection and replication relies on host lipid metabolism. HCV proteins interact and associate with lipid droplets to facilitate virion assembly and production. Besides,circulating infective particles are associated with verylow-density lipoprotein. On the other hand,higher serum lipid levels have been associated with sustained viral response to pegylated interferon and ribavirin therapy in chronic HCV infection,suggesting a relevant role in viral clearance for host proteins. Host and viral genetic factors play an essential role in chronic infection. Lipid metabolism is hijacked by viral infection and could determine the success of viral replication. Recently development of direct acting antiviral agents has shown a very high efficacy( 90%) in sustained viral response rates even for cirrhotic patients and most of the viral genotypes. HCV RNA clearance induced by Sofosbuvir has been associated with an increased concentration and size of the low-density lipoprotein particles. In this review,host genetic factors,viral factors and the interaction between them will be depicted to clarify the major issues involved in viral infection and lipid metabolism.     

Immunometabolic Effect of Cholesterol in Hepatitis C Infection: Implications in Clinical Management and Antiviral Therapy

Hepatitis C virus (HCV) is a lipid-enveloped virion particle that causes infection to the liver, and as part of its life cycle, it disrupts the host lipid metabolic machinery, particularly the cholesterol synthesis pathway. The innate immune response generated by liver resident immune cells is responsible for successful viral eradication. Unfortunately, most patients fail to eliminate HCV and progress to chronic infection. Chronic infection is associated with hepatic fat accumulation and inflammation that triggers fibrosis, cirrhosis, and eventually hepatocellular carcinoma. Despite that the current direct-acting antiviral agents have increased the cure rate of HCV infection, viral genotype and the host genetic background influence both the immune response and lipid metabolism. In this context, recent evidence has shown that cholesterol and its derivatives such as oxysterols might modulate and potentialize the hepatic innate immune response generated against HCV. The impairment of the HCV life cycle modulated by serum cholesterol could be relevant for the clinical management of HCV-infected patients before and after treatment. Alongside, cholesterol levels are modulated either by genetic variations in IL28B, ApoE, and LDLR or by dietary components. Indeed, some nutrients such as unsaturated fatty acids have demonstrated to be effective against HCV replication. Thus, cholesterol modifications may be considered as a new adjuvant strategy for HCV infection therapy by providing a biochemical tool that guides treatment decisions, an improved treatment response and favoring viral clearance. Herein, the mechanisms by which cholesterol contributes to the immune response against HCV infection and how genetic and environmental factors may affect this role are reviewed.     

Effects of hypolipidemic agent nordihydroguaiaretic acid on lipid droplets and hepatitis C virus

Hepatitis C virus (HCV) relies on host lipid metabolic pathways for its replication, assembly, secretion, and entry. HCV induces de novo lipogenesis, inhibits β-oxidation, and lipoprotein export resulting in a lipid-enriched cellular environment critical for its proliferation. We investigated the effects of a hypolipidemic agent, nordihydroguaiaretic acid (NDGA), on host lipid/fatty acid synthesis and HCV life cycle. NDGA negated the HCV-induced alteration of host lipid homeostasis. NDGA decreased sterol regulatory element binding protein (SREBP) activation and enhanced expression of genes involved in β-oxidation. NDGA inhibited very low-density lipoprotein (VLDL) secretion by affecting mediators of VLDL biosynthesis. Lipid droplets (LDs), the neutral lipid storage organelles, play a key role in HCV morphogenesis. HCV induces accumulation and perinuclear distribution of LDs, whereas NDGA most notably reduced the overall number and increased the average size of LDs. The antiviral effects of NDGA resulted in reduced HCV replication and secretion. Conclusion: NDGA-mediated alterations of host lipid metabolism, LD morphology, and VLDL transport appear to negatively influence HCV proliferation.     

Roles of lipoprotein receptors in the entry of hepatitis C virus

Infection by hepatitis C virus(HCV), a plus-stranded RNA virus that can cause cirrhosis and hepatocellular carcinoma, is one of the major health problems in the world. HCV infection is considered as a multistep complex process and correlated with abnormal metabolism of lipoprotein. In addition, virus attacks hepatocytes by the initial attaching viral envelop glycoprotein E1/E2 to receptors of lipoproteins on host cells. With the development of HCV model system, mechanisms of HCV cell entry through lipoprotein uptake and its receptor have been extensively studied in detail. Here we summarize recent knowledge about the role of lipoprotein receptors, scavenger receptor class B type Ⅰ and low-density lipoprotein receptor in the entry of HCV, providing a foundation of novel targeting therapeutic tools against HCV infection.     

Human apolipoprotein E peptides inhibit hepatitis C virus entry by blocking virus binding

Hepatitis C virus (HCV) entry is a multiple-step process involving a number of host factors and hence represents a promising target for new antiviral drug development. In search of novel inhibitors of HCV infection, we found that a human apolipoprotein E (apoE) peptide, hEP, containing both a receptor binding fragment and a lipid binding fragment of apoE specifically blocked the entry of cell culture grown HCV (HCVcc) at submicromolar concentrations. hEP caused little cytotoxicity in vitro and remained active even if left 24 hours in cell culture. Interestingly, hEP inhibited neither human immunodeficiency virus (HIV)-HCV pseudotypes (HCVpp) nor HIV and Dengue virus (DENV) infection. Further characterization mapped the anti-HCV activity to a 32-residue region that harbors the receptor binding domain of apoE, but this fragment must contain a cysteine residue at the N-terminus to mediate dimer formation. The anti-HCV activity of the peptide appears to be dependent on both its length and sequence and correlates with its ability to bind lipids. Finally, we demonstrated that the apoE-derived peptides directly blocked the binding of both HCVcc and patient serum-derived virus to hepatoma cells as well as primary human hepatocytes. CONCLUSION: apoE peptides potently inhibit HCV infection and suggest a direct role of apoE in mediating HCV entry. Our findings also highlight the potential of developing apoE mimetic peptides as novel HCV entry inhibitors by targeting HCV-host interactions.     

Efficient replication of primary or culture hepatitis C virus isolates in human liver slices: A relevant ex vivo model of liver infection

The development of human cultured hepatitis C virus (HCV) replication-permissive hepatocarcinoma cell lines has provided important new virological tools to study the mechanisms of HCV infection; however, this experimental model remains distantly related to physiological and pathological conditions. Here, we report the development of a new ex vivo model using human adult liver slices culture, demonstrating, for the first time, the ability of primary isolates to undergo de novo viral replication with the production of high-titer infectious virus as well as Japanese fulminant hepatitis type 1, H77/C3, and Con1/C3. This experimental model was employed to demonstrate HCV neutralization or HCV inhibition, in a dose-dependent manner, either by cluster of differentiation 81 or envelope protein 2-specific antibodies or convalescent serum from a recovered HCV patient or by antiviral drugs. Conclusion: This new ex vivo model represents a powerful tool for studying the viral life cycle and dynamics of virus spread in native tissue and also allows one to evaluate the efficacy of new antiviral drugs. (HEPATOLOGY 2012;56:861-872).     

Biología molecular aplicada del virus de la hepatitis C

Since the discovery of the hepatitis C virus (HCV), a plethora of experimental models have evolved, allowing the virus's life cycle and the pathogenesis of associated liver diseases to be investigated. These models range from inoculation of cultured cells with serum from patients with hepatitis C to the use of surrogate models for the study of specific stages of the HCV life cycle: retroviral pseudoparticles for the study of HCV entry, replicons for the study of HCV replication, and the HCV cell culture model, which reproduces the entire life cycle (replication and production of infectious particles). The use of these tools has been and remains crucial to identify potential therapeutic targets in the different stages of the virus's life cycle and to screen new antiviral drugs. A clear example is the recent approval of two viral protease inhibitors (boceprevir and telaprevir) in combination with pegylated interferon and ribavirin for the treatment of chronic hepatitis C. This review analyzes the advances made in the molecular biology of HCV and highlights possible candidates as therapeutic targets for the treatment of HCV infection.     

Hepatitis C virus infection: in vivo and in vitro models

Summary.  Major advances in the understanding of the molecular biology of hepatitis C virus (HCV) have been made recently. While the chimpanzee is the only established animal model of HCV infection, several in vivo and in vitro models have been established that allow us to study various aspects of the viral life cycle. In particular, the replicon system and the production of recombinant infectious virions revolutionized the investigation of HCV-RNA replication and rendered all steps of the viral life cycle, including entry and release of viral particles, amenable to systematic analysis. In the following we will review the different in vivo and in vitro models of HCV infection.