Identification of the Niemann-Pick C1-like 1 cholesterol absorption receptor as a new hepatitis C virus entry factor

Oligonucleotide-Lipid Conjugates Forming G-Quadruplex Structures Are Potent and Pangenotypic Hepatitis C Virus Entry Inhibitors In Vitro and Ex Vivo

A hepatitis C virus (HCV) epidemic affecting HIV-infected men who have sex with men (MSM) is expanding worldwide. In spite of the improved cure rates obtained with the new direct-acting antiviral drug (DAA) combinations, the high rate of reinfection within this population calls urgently for novel preventive interventions. In this study, we determined in cell culture and ex vivo experiments with human colorectal tissue that lipoquads, G-quadruplex DNA structures fused to cholesterol, are efficient HCV pangenotypic entry and cell-to-cell transmission inhibitors. Thus, lipoquads may be promising candidates for the development of rectally applied gels to prevent HCV transmission.

Cyanobacterial lectins characteristics and their role as antiviral agents

Lectins are ubiquitous proteins/glycoproteins of non-immune origin that bind reversibly to carbohydrates in non-covalent and highly specific manner. These lectin-glycan interactions could be exploited for establishment of novel therapeutics, targeting the adherence stage of viruses and thus helpful in eliminating wide spread viral infections. Here the review focuses on the haemagglutination activity, carbohydrate specificity and characteristics of cyanobacterial lectins. Cyanobacterial lectins exhibiting high specificity towards mannose or complex glycans have potential role as anti-viral agents. Prospective role of cyanobacterial lectins in targeting various diseases of worldwide concern such as HIV, hepatitis, herpes, influenza and ebola viruses has been discussed extensively. The review also lays emphasis on recent studies involving structural analysis of glycan-lectin interactions which in turn influence their mechanism of action. Altogether, the promising approach of these cyanobacterial lectins provides insight into their use as antiviral agents.

Hepatitis C Virus-Genotype 3: Update on Current and Emergent Therapeutic Interventions

PURPOSE OF REVIEW

Direct-acting antiviral agents (DAAs) have markedly improved the prognosis of hepatitis C virus (HCV)-genotype 3 (GT3), a highly prevalent infection worldwide. However, in patients with hepatic fibrosis, cirrhosis, or hepatocellular carcinoma (HCC), GT3 infection presents a treatment challenge compared with other genotypes. The dependence of the HCV life cycle on host lipid metabolism suggests the possible utility of targeting host cellular factors for combination anti-HCV therapy. We discuss current and emergent DAA regimens for HCV-GT3 treatment. We then summarize recent research findings on the reliance of HCV entry, replication, and virion assembly on host lipid metabolism.

RECENT FINDINGS

Current HCV treatment guidelines recommend the use of daclatasvir plus sofosbuvir (DCV/SOF) or sofosbuvir plus velpatasvir (SOF/VEL) for the management of GT3 based upon clinical efficacy [≥88% overall sustained virological response (SVR)] and tolerability. Potential future DAA options, such as SOF/VEL co-formulated with GS-9857, also look promising in treating cirrhotic GT3 patients. However, HCV resistance to DAAs will likely continue to impact the therapeutic efficacy of interferon-free treatment regimens. Disruption of HCV entry by targeting required host cellular receptors shows potential in minimizing HCV resistance and broadening therapeutic options for certain subpopulations of GT3 patients. The use of cholesterol biosynthesis and transport inhibitors may also improve health outcomes for GT3 patients when used synergistically with DAAs. Due to the morbidity and mortality associated with HCV-GT3 infection compared to other genotypes, efforts should be made to address current limitations in the therapeutic prevention and management of HCV-GT3 infection.

Claudin-targeted drug development using anti-claudin monoclonal antibodies to treat hepatitis and cancer

The 27-member family of tetraspan membrane proteins known as claudins (CLDNs) is a major component of tight junctions. A series of studies elucidating the relationship between CLDNs and various pathological conditions has provided new insights into drug development. For instance, CLDN-1 may be a potent target for epidermal absorption of drugs and for treating hepatitis C virus (HCV) infection. CLDN-4 may be a target for treating cancer. Because CLDNs are also expressed in various normal tissues, safety and efficacy evaluations are critical for translational research. We previously developed several anti-CLDN antibodies and have established proof of concept for CLDN-targeted drug development using these reagents. Here, we provide an overview of CLDN-1 as a target for improving epidermal drug absorption and preventing HCV infection and of CLDN-4 as a target for anticancer therapeutics.

Anti-hepatitis C virus strategy targeting host entry factor claudin-1

Chronic hepatitis C virus (HCV) infection is a major threat to global public health, because it is significantly correlated with the development of severe liver diseases including cirrhosis and hepatocellular carcinomas. Host molecules as well as viral factors are promising targets for anti-HCV preventive and therapeutic strategies. Multiple host factors such as CD81, SRBI, claudin-1, and occludin are involved in HCV entry into hepatocytes. In this paper, I first introduce our anti-HCV strategy targeting for host tight junction protein claudin-1. And this review also summarizes developments of other entry inhibitors to prevent initiation of HCV infection and spread. Entry inhibitors might be useful in blocking primary infections, such those as after liver transplantation, and in combination therapies with other anti-HCV agents such as direct-acting antivirals.

Hepatitis C virus may have an entero-hepatic cycle which could be blocked with ezetimibe

Hepatitis C virus can lead to chronic infection, cirrhosis and hepatocellular carcinoma. With more than 170 million people infected worldwide, eradication remains a challenge even with the revolutionary current direct antiviral agents (DAAs). The risk of resistance, the safety profile in some populations, the genotype specificity and the high price of current DAAs explain why there is still interest in developing host targeting agents (HTA) that may help overcome some of these difficulties. Specifically, targeting the entry of HCV to the cell seems like a promising strategy. Recently it has been shown that the cholesterol transporter NPC1L1, a protein located in the small bowel epithelium and in the canalicular membrane of the hepatocyte is also an HCV receptor. Just as this protein is key in the entero-hepatic cycle of cholesterol, we hypothesize that there is an entero-hepatic cycle of HCV that could be disrupted by blocking NPC1L1 with ezetimibe, an already approved and readily available safe drug. Ezetimibe, either alone or in combination with DAAs, could decrease relapse rates, reduce resistance and even make treatments cheaper.

Detection of high biliary and fecal viral loads in patients with chronic hepatitis C virus infection

BACKGROUND

The life cycle of the hepatitis C virus (HCV) is closely associated with lipid metabolism. Recently, NPC1L1 (a cholesterol transporter) has been reported to function as an HCV receptor. This receptor is expressed in the hepatocyte canalicular membrane and in the intestine; serving as a key transporter for the cholesterol enterohepatic cycle.

OBJECTIVES

We hypothesized that HCV might have a similar cycle, so we aimed to study the presence of HCV in bile and stools of infected patients.

MATERIALS AND METHODS

Blood, feces, and duodenal bile samples were collected from patients infected with HCV. The biliary viral load was normalized to the bile salt concentration of each sample and the presence of HCV core protein was also evaluated. A total of 12 patients were recruited. HCV RNA was detected in the bile from ten patients.

RESULTS

The mean viral load was 2.5log10IU/60mg bile salt. In the stool samples, HCV RNA was detected in ten patients (mean concentration 2.7log10IU/g of feces).

CONCLUSIONS

HCV RNA is readily detectable and is present at relatively high concentrations in the bile and stool samples of infected patients. This may be relevant as a source of infection in men who have sex with men. Biliary HCV secretion may perhaps play a role in the persistence of viral infection via an enterohepatic cycle of the virus or intrahepatic spread.

Recent advances in hepatocellular carcinoma therapy

Hepatocellular carcinoma (HCC), also called malignant hepatoma, is one of the deadliest cancers due to its complexities, reoccurrence after surgical resection, metastasis and heterogeneity. Incidence and mortality of HCC are increasing in Western countries and are expected to rise as a consequence of the obesity epidemic. Multiple factors trigger the initiation and progression of HCC including chronic alcohol consumption, viral hepatitis B and C infection, metabolic disorders and age. Although Sorafenib is the only FDA approved drug for the treatment of HCC, numerous treatment modalities such as transcatheter arterial chemoembolization/transarterial chemoembolization (TACE), radiotherapy, locoregional therapy and chemotherapy have been tested in the clinics. Polymeric nanoparticles, liposomes, and micelles carrying small molecules, proteins, peptides and nucleic acids have attracted great attention for the treatment of various cancers including HCC. Herein, we discuss the pathogenesis of HCC in relation to its various recent treatment methodologies using nanodelivery of monoclonal antibodies (mAbs), small molecules, miRNAs and peptides. Synopsis of recent clinical trials of mAbs and peptide drugs has been presented with a broad overview of the pathogenesis of the disease and treatment efficacy.

Mice Expressing Minimally Humanized CD81 and Occludin Genes Support Hepatitis C Virus Uptake In Vivo

Hepatitis C virus (HCV) causes chronic infections in at least 150 million individuals worldwide. HCV has a narrow host range and robustly infects only humans and chimpanzees. The underlying mechanisms for this narrow host range are incompletely understood. At the level of entry, differences in the amino acid sequences between the human and mouse orthologues of two essential host factors, the tetraspanin CD81 and the tight junction protein occludin (OCLN), explain, at least in part, HCV's limited ability to enter mouse hepatocytes. We have previously shown that adenoviral or transgenic overexpression of human CD81 and OCLN facilitates HCV uptake into mouse hepatocytes in vitro and in vivo In efforts to refine these models, we constructed knock-in mice in which the second extracellular loops of CD81 and OCLN were replaced with the respective human sequences, which contain the determinants that are critical for HCV uptake. We demonstrate that the humanized CD81 and OCLN were expressed at physiological levels in a tissue-appropriate fashion. Mice bearing the humanized alleles formed normal tight junctions and did not exhibit any immunologic abnormalities, indicating that interactions with their physiological ligands were intact. HCV entry factor knock-in mice take up HCV with an efficiency similar to that in mice expressing HCV entry factors transgenically or adenovirally, demonstrating the utility of this model for studying HCV infection in vivo IMPORTANCE: At least 150 million individuals are chronically infected with hepatitis C virus (HCV). Chronic hepatitis C can result in progressive liver disease and liver cancer. New antiviral treatments can cure HCV in the majority of patients, but a vaccine remains elusive. To gain a better understanding of the processes culminating in liver failure and cancer and to prioritize vaccine candidates more efficiently, small-animal models are needed. Here, we describe the characterization of a new mouse model in which the parts of two host factors that are essential for HCV uptake, CD81 and occludin (OCLN), which differ between mice and humans, were humanized. We demonstrate that such minimally humanized mice develop normally, express the modified genes at physiological levels, and support HCV uptake. This model is of considerable utility for studying viral entry in the three-dimensional context of the liver and to test approaches aimed at preventing HCV entry.

Visualizing the Essential Role of Complete Virion Assembly Machinery in Efficient Hepatitis C Virus Cell-to-Cell Transmission by a Viral Infection-Activated Split-Intein-Mediated Reporter System

Hepatitis C virus (HCV) infects 2 to 3% of the world population and is a leading cause of liver diseases such as fibrosis, cirrhosis, and hepatocellular carcinoma. Many aspects of HCV study, ranging from molecular virology and antiviral drug development to drug resistance profiling, were supported by straightforward assays of HCV replication and infection. Among these assays, the HCV-dependent fluorescence relocalization (HDFR) system allowed live-cell visualization of infection without modifying the viral genome, but this strategy required careful recognition of the fluorescence relocalization pattern for its high fluorescence background in the cytoplasm. In this study, to achieve background-free visualization of HCV infection, a viral infection-activated split-intein-mediated reporter system (VISI) was devised. Uninfected Huh7.5.1-VISI cells show no background signal, while HCV infection specifically illuminates the nuclei of infected Huh7.5.1-VISI cells with either green fluorescent protein (GFP) or mCherry. Combining VISI-GFP and VISI-mCherry systems, we revisited HCV cell-to-cell transmission with clear-cut distinction of donor and recipient cells in a live-cell manner. Independently of virion assembly, exosomes have been reported to transfer HCV subgenomic RNA to initiate replication in uninfected cells, which suggested an assembly-free pathway. However, our data demonstrated that HCV structural genes and the p7 gene were essential for not only cell-free infectivity but also cell-to-cell transmission. Additionally, depletion of apolipoprotein E (ApoE) from donor cells but not from recipient cells significantly reduced HCV cell-to-cell transmission efficiency. In summary, we developed a background-free cell-based reporter system for convenient live-cell visualization of HCV infection, and our data indicate that complete HCV virion assembly machinery is essential for both cell-free and cell-to-cell transmission.

IMPORTANCE

Hepatitis C virus (HCV) infects hepatocytes via two pathways: cell-free infection and cell-to-cell transmission. Structural modules of the HCV genome are required for production of infectious cell-free virions; however, the role of specific genes within the structural module in cell-to-cell transmission is not clearly defined. Our data demonstrate that deletion of core, E1E2, and p7 genes individually results in no HCV cell-to-cell transmission and that ApoE knockdown from donor cells causes less-efficient cell-to-cell transmission. Thus, this work indicates that the complete HCV assembly machinery is required for HCV cell-to-cell transmission. At last, this work presents an optimized viral infection-activated split-intein-mediated reporter system for easy live-cell monitoring of HCV infection.

TIM-1 Promotes Hepatitis C Virus Cell Attachment and Infection

Human TIM and TAM family proteins were recently found to serve as phosphatidylserine (PS) receptors which promote infections by many different viruses, including dengue virus, West Nile virus, Ebola virus, Marburg virus, and Zika virus. In the present study, we provide substantial evidence demonstrating that TIM-1 is important for efficient infection by hepatitis C virus (HCV). The knockdown of TIM-1 expression significantly reduced HCV infection but not HCV RNA replication. Likewise, TIM-1 knockout in Huh-7.5 cells remarkably lowered HCV cell attachment and subsequent HCV infection. More significantly, the impairment of HCV infection in the TIM-1 knockout cells could be restored completely by ectopic expression of TIM-1 but not TIM-3 or TIM-4. Additionally, HCV infection and cell attachment were inhibited by PS but not by phosphatidylcholine (PC), demonstrating that TIM-1-mediated enhancement of HCV infection is PS dependent. The exposure of PS on the HCV envelope was confirmed by immunoprecipitation of HCV particles with a PS-specific monoclonal antibody. Collectively, these findings demonstrate that TIM-1 promotes HCV infection by serving as an attachment receptor for binding to PS exposed on the HCV envelope.

IMPORTANCE

TIM family proteins were recently found to enhance infections by many different viruses, including several members of the Flaviviridae family. However, their importance in HCV infection has not previously been examined experimentally. The TIM family proteins include three members in humans: TIM-1, TIM-3, and TIM-4. The findings derived from our studies demonstrate that TIM-1, but not TIM-3 or TIM-4, promotes HCV infection by functioning as an HCV attachment factor. Knockout of the TIM-1 gene resulted in a remarkable reduction of HCV cell attachment and infection. PS-containing liposomes blocked HCV cell attachment and subsequent HCV infection. HCV particles could also be precipitated with a PS-specific monoclonal antibody. These findings suggest that TIM-1 and its binding ligand, PS, may serve as novel targets for antiviral intervention.

Infection of Hepatocytes With HCV Increases Cell Surface Levels of Heparan Sulfate Proteoglycans, Uptake of Cholesterol and Lipoprotein, and Virus Entry by Up-regulating SMAD6 and SMAD7

BACKGROUND & AIMS

The signaling molecule and transcriptional regulator SMAD6, which inhibits the transforming growth factor β signaling pathway, is required for infection of hepatocytes by hepatitis C virus (HCV). We investigated the mechanisms by which SMAD6 and another inhibitory SMAD (SMAD7) promote HCV infection in human hepatoma cells and hepatocytes.

METHODS

We infected Huh7 and Huh7.5.1 cells and primary human hepatocytes with Japanese fulminant hepatitis-1 (JFH1) HCV cell culture system (HCVcc). We then measured HCV binding, intracellular levels of HCV RNA, and expression of target genes. We examined HCV entry in HepG2/microRNA (miR) 122/CD81 cells, which support entry and replication of HCV, were transfected these cells with small interfering RNAs targeting inhibitory SMADs to analyze gene expression profiles. Uptake of labeled low-density lipoprotein (LDL) and cholesterol was measured. Cell surface proteins were quantified by flow cytometry. We obtained liver biopsy samples from 69 patients with chronic HCV infection and 19 uninfected individuals (controls) and measured levels of syndecan 1 (SDC1), SMAD7, and SMAD6 messenger RNAs (mRNAs).

RESULTS

Small interfering RNA knockdown of SMAD6 blocked the binding and infection of hepatoma cell lines and primary human hepatocytes by HCV, whereas SMAD6 overexpression increased HCV infection. We found levels of mRNAs encoding heparan sulfate proteoglycans (HSPGs), particularly SDC1 mRNA, and cell surface levels of heparan sulfate to be reduced in cells after SMAD6 knockdown. SMAD6 knockdown also reduced transcription of genes encoding lipoprotein and cholesterol uptake receptors, including the LDL receptor (LDLR), the very LDLR, and the scavenger receptor class B member 1 in hepatocytes; knockdown of SMAD6 also inhibited cell uptake of cholesterol and lipoprotein. Overexpression of SMAD6 increased the expression of these genes. Similar effects were observed with knockdown and overexpression of SMAD7. In addition, HCV infection of cells increased the expression of SMAD6, which required the activity of nuclear factor-κB, but not transforming growth factor β. Liver tissues from patients with chronic HCV infection had significantly higher levels of SMAD6, SMAD7, and HSPG mRNAs than controls.

CONCLUSIONS

In studies of hepatoma cell lines and primary human hepatocytes, we found that infection with HCV leads to activation of nuclear factor-κB, resulting in increased expression of SMAD6 and SMAD7. Up-regulation of SMAD6 and SMAD7 induces the expression of HSPGs, such as SDC1, as well as LDLR, very LDLR, and the scavenger receptor class B member 1, which promote HCV entry and propagation, as well as cellular uptake of cholesterol and lipoprotein.

Apolipoprotein B100 is required for hepatitis C infectivity and Mipomersen inhibits hepatitis C

AIM

To characterize the role of apolipoprotein B100 (apoB100) in hepatitis C viral (HCV) infection.

METHODS

In this study, we utilize a gene editing tool, transcription activator-like effector nucleases (TALENs), to generate human hepatoma cells with a stable genetic deletion of APOB to assess of apoB in HCV. Using infectious cell culture-competent HCV, viral pseudoparticles, replicon models, and lipidomic analysis we determined the contribution of apoB to each step of the viral lifecycle. We further studied the effect of mipomersen, an FDA-approved antisense inhibitor of apoB100, on HCV using in vitro cell-culture competent HCV and determined its impact on viral infectivity with the TCID50 method.

RESULTS

We found that apoB100 is indispensable for HCV infection. Using the JFH-1 fully infectious cell-culture competent virus in Huh 7 hepatoma cells with TALEN-mediated gene deletion of apoB (APOB KO), we found a significant reduction in HCV RNA and protein levels following infection. Pseudoparticle and replicon models demonstrated that apoB did not play a role in HCV entry or replication. However, the virus produced by APOB KO cells had significantly diminished infectivity as measured by the TCID-50 method compared to wild-type virus. Lipidomic analysis demonstrated that these virions have a fundamentally altered lipidome, with complete depletion of cholesterol esters. We further demonstrate that inhibition of apoB using mipomersen, an FDA-approved anti-sense oligonucleotide, results in a potent anti-HCV effect and significantly reduces the infectivity of the virus.

CONCLUSION

ApoB is required for the generation of fully infectious HCV virions, and inhibition of apoB with mipomersen blocks HCV. Targeting lipid metabolic pathways to impair viral infectivity represents a novel host targeted strategy to inhibit HCV.

Claudins in viral infection: from entry to spread

Tight junctions are critically important for many physiological functions, including the maintenance of cell polarity, regulation of paracellular permeability, and involvement in signal transduction pathways to regulate integral cellular processes. Furthermore, tight junctions enable epithelial cells to form physical barriers, which act as an innate immune mechanism that can impede viral infection. Viruses, in turn, have evolved mechanisms to exploit tight junction proteins to gain access to cells or spread through tissues in an infected host. Claudin family proteins are integral components of tight junctions and are thought to play crucial roles in regulating their permeability. Claudins have been implicated in the infection process of several medically important human pathogens, including hepatitis C virus, dengue virus, West Nile virus, and human immunodeficiency virus, among others. In this review, we summarize the role of claudins in viral infections and discuss their potential as novel antiviral targets. A better understanding of claudins during viral infection may provide insight into physiological roles of claudins and uncover novel therapeutic antiviral strategies.

Expanding the Host Range of Hepatitis C Virus through Viral Adaptation

Hepatitis C virus (HCV) species tropism is incompletely understood. We have previously shown that at the level of entry, human CD81 and occludin (OCLN) comprise the minimal set of human factors needed for viral uptake into murine cells. As an alternative approach to genetic humanization, species barriers can be overcome by adapting HCV to use the murine orthologues of these entry factors. We previously generated a murine tropic HCV (mtHCV or Jc1/mCD81) strain harboring three mutations within the viral envelope proteins that allowed productive entry into mouse cell lines. In this study, we aimed to characterize the ability of mtHCV to enter and infect mouse hepatocytes in vivo and in vitro. Using a highly sensitive, Cre-activatable reporter, we demonstrate that mtHCV can enter mouse hepatocytes in vivo in the absence of any human cofactors. Viral entry still relied on expression of mouse CD81 and SCARB1 and was more efficient when mouse CD81 and OCLN were overexpressed. HCV entry could be significantly reduced in the presence of anti-HCV E2 specific antibodies, suggesting that uptake of mtHCV is dependent on viral glycoproteins. Despite mtHCV’s ability to enter murine hepatocytes in vivo, we did not observe persistent infection, even in animals with severely blunted type I and III interferon signaling and impaired adaptive immune responses. Altogether, these results establish proof of concept that the barriers limiting HCV species tropism can be overcome by viral adaptation. However, additional viral adaptations will likely be needed to increase the robustness of a murine model system for hepatitis C.

At least 150 million individuals are chronically infected with HCV and are at risk of developing serious liver disease. Despite the advent of effective antiviral therapy, the frequency of chronic carriers has only marginally decreased. A major roadblock in developing a vaccine that would prevent transmission is the scarcity of animal models that are susceptible to HCV infection. It is poorly understood why HCV infects only humans and chimpanzees. To develop an animal model for hepatitis C, previous efforts focused on modifying the host environment of mice, for example, to render them more susceptible to HCV infection. Here, we attempted a complementary approach in which a laboratory-derived HCV variant was tested for its ability to infect mice. We demonstrate that this engineered HCV strain can enter mouse liver cells but does not replicate efficiently. Thus, additional adaptations are likely needed to construct a robust animal model for HCV.

Genetic variations of the NPC1L1 gene associated with hepatitis C virus (HCV) infection and biochemical characteristics of HCV patients in China

OBJECTIVES

About 2% of the world population is infected with hepatitis C virus (HCV), a leading cause of hepatic cirrhosis and hepatocellular carcinoma. The Niemann-Pick C1-like 1 cholesterol absorption receptor (NPC1L1) was recently identified to be an important factor for HCV entry into host cells. Whether genetic variations of the NPC1L1 gene are associated with HCV infection is unknown.

METHODS

In this study, five single nucleotide polymorphisms (SNPs) of the NPC1L1 gene were analyzed in 261 HCV-infected individuals and 265 general controls from Yunnan Province, China.

RESULTS

No significant differences were identified in genotypes or alleles of the SNPs between the two groups. After constructing haplotypes based on the five SNPs, a significant difference between HCV-infected individuals and general controls was shown for two haplotypes. Haplotype GCCTT appeared to be a protective factor and haplotype GCCCT was a risk factor for HCV-infected individuals. Genotypes of four SNPs correlated with biochemical characteristics of HCV-infected persons. Genotypes of SNPs rs799444 and rs2070607 were correlated with total bilirubin. Genotype TT of rs917098 was a risk factor for the gamma-glutamyltransferase level. Furthermore, HCV-infected individuals carrying genotype GG of rs41279633 showed statistically higher gamma-glutamyltransferase levels than HCV-infected persons with GT and TT.

CONCLUSION

The results of this study identified the association between genetic susceptibility of the NPC1L1 gene and HCV infection, as well as biochemical characteristics of HCV-infected persons in Yunnan, China.

The history of hepatitis C virus (HCV): Basic research reveals unique features in phylogeny, evolution and the viral life cycle with new perspectives for epidemic control

The discovery of hepatitis C virus (HCV) in 1989 permitted basic research to unravel critical components of a complex life cycle for this important human pathogen. HCV is a highly divergent group of viruses classified in 7 major genotypes and a great number of subtypes, and circulating in infected individuals as a continuously evolving quasispecies destined to escape host immune responses and applied antivirals. Despite the inability to culture patient viruses directly in the laboratory, efforts to define the infectious genome of HCV resulted in development of experimental recombinant in vivo and in vitro systems, including replicons and infectious cultures in human hepatoma cell lines. And HCV has become a model virus defining new paradigms in virology, immunology and biology. For example, HCV research discovered that a virus could be completely dependent on microRNA for its replication since microRNA-122 is critical for the HCV life cycle. A number of other host molecules critical for HCV entry and replication have been identified. Thus, basic HCV research revealed important molecules for development of host targeting agents (HTA). The identification and characterization of HCV encoded proteins and their functional units contributed to the development of highly effective direct acting antivirals (DAA) against the NS3 protease, NS5A and the NS5B polymerase. In combination, these inhibitors have since 2014 permitted interferon-free therapy with cure rates above 90% among patients with chronic HCV infection; however, viral resistance represents a challenge. Worldwide control of HCV will most likely require the development of a prophylactic vaccine, and numerous candidates have been pursued. Research characterizing features critical for antibody-based virus neutralization and T cell based virus elimination from infected cells is essential for this effort. If the world community promotes an ambitious approach by applying current DAA broadly, continues to develop alternative viral- and host- targeted antivirals to combat resistant variants, and invests in the development of a vaccine, it would be possible to eradicate HCV. This would prevent about 500 thousand deaths annually. However, given the nature of HCV, the millions of new infections annually, a high chronicity rate, and with over 150 million individuals with chronic infection (which are frequently unidentified), this effort remains a major challenge for basic researchers, clinicians and communities.

Successful disabling of the 5' UTR of HCV using adeno-associated viral vectors to deliver modular multimeric primary microRNA mimics

Chronic hepatitis C virus (HCV) infection is a major health concern and is strongly associated with cirrhosis, hepatocellular carcinoma and liver-related mortality. The HCV genome is the template for both protein translation and viral replication and, being RNA, is amenable to direct genetic silencing by RNA interference (RNAi). HCV is a highly mutable virus and is capable of escaping RNAi-mediated silencing. This has highlighted the importance of developing RNAi-based therapy that simultaneously targets multiple regions of the HCV genome. To develop a multi-targeting RNAi activator, a novel approach for the generation of anti-HCV gene therapy was investigated. Five artificial primary miRNA (pri-miR) were each designed to mimic the naturally occurring monomeric pri-miR-31. Potent knockdown of an HCV reporter was seen with four of the five constructs and were processed according to the intended design. The design of the individual pri-miR mimics enabled the modular assembly into multimeric mimics of any possible conformation. Consequently the four potent pri-miR mimics were used to generate polycistronic cassettes, which showed impressive silencing of an HCV target. To further their application as a gene therapy, recombinant adeno-associated viral (rAAV) vectors that express the polycistronic pri-miR mimics were generated. All AAV-delivered anti-HCV pri-miR mimics significantly knocked down the expression of an HCV target and showed inhibition of HCV replicon replication. Here we describe a protocol for the generation of therapeutic rAAVs that express modular polycistronic pri-miR cassettes allowing for rapid alteration and generation of tailored therapeutic constructs against HCV.

Modeling Viral Spread

The way in which a viral infection spreads within a host is a complex process that is not well understood. Different viruses, such as human immunodeficiency virus type 1 and hepatitis C virus, have evolved different strategies, including direct cell-to-cell transmission and cell-free transmission, to spread within a host. To what extent these two modes of transmission are exploited in vivo is still unknown. Mathematical modeling has been an essential tool to get a better systematic and quantitative understanding of viral processes that are difficult to discern through strictly experimental approaches. In this review, we discuss recent attempts that combine experimental data and mathematical modeling in order to determine and quantify viral transmission modes. We also discuss the current challenges for a systems-level understanding of viral spread, and we highlight the promises and challenges that novel experimental techniques and data will bring to the field.

Effect of Quercetin on Hepatitis C Virus Life Cycle: From Viral to Host Targets

Quercetin is a natural flavonoid, which has been shown to have anti hepatitis C virus (HCV) properties. However, the exact mechanisms whereby quercetin impacts the HCV life cycle are not fully understood. We assessed the effect of quercetin on different steps of the HCV life cycle in Huh-7.5 cells and primary human hepatocytes (PHH) infected with HCVcc. In both cell types, quercetin significantly decreased i) the viral genome replication; ii) the production of infectious HCV particles and iii) the specific infectivity of the newly produced viral particles (by 85% and 92%, Huh7.5 and PHH respectively). In addition, when applied directly on HCV particles, quercetin reduced their infectivity by 65%, suggesting that it affects the virion integrity. Interestingly, the HCV-induced up-regulation of diacylglycerol acyltransferase (DGAT) and the typical localization of the HCV core protein to the surface of lipid droplets, known to be mediated by DGAT, were both prevented by quercetin. In conclusion, quercetin appears to have direct and host-mediated antiviral effects against HCV.

Polyanionic carbosilane dendrimers prevent hepatitis C virus infection in cell culture

Hepatitis C virus (HCV) infection is a major biomedical problem worldwide. Although new direct antiviral agents (DAAs) have been developed for the treatment of chronic HCV infection, the potential emergence of resistant virus variants and the difficulties to implement their administration worldwide make the development of novel antiviral agents an urgent need. Moreover, no effective vaccine is available against HCV and transmission of the virus still occurs particularly when prophylactic measures are not taken. We used a cell-based system to screen a battery of polyanionic carbosilane dendrimers (PCDs) to identify compounds with antiviral activity against HCV and show that they inhibit effective virus adsorption of major HCV genotypes. Interestingly, one of the PCDs irreversibly destabilized infectious virions. This compound displays additive effect in combination with a clinically relevant DAA, sofosbuvir. Our results support further characterization of these molecules as nanotools for the control of hepatitis C virus spread.

Hepatitis C virus G1b infection decreases the number of small low-density lipoprotein particles

AIM: To investigate how hepatitis C virus (HCV) G1b infection influences the particle number of lipoproteins.

METHODS: The numbers of lipoprotein particles in fasting sera from 173 Japanese subjects, 82 with active HCV G1b infection (active HCV group) and 91 with cleared HCV infection (SVR group), were examined. Serum lipoprotein was fractionated by high-performance liquid chromatography into twenty fractions. The cholesterol and triglyceride concentrations in each fraction were measured using LipoSEARCH. The number of lipoprotein particles in each fraction was calculated using a newly developed algorithm, and the relationship between chronic HCV G1b infection and the lipoprotein particle number was determined by multiple linear regression analysis.

RESULTS: The median number of low-density lipoprotein (LDL) particles was significantly lower in the active HCV group [1182 nmol/L, interquartile range (IQR): 444 nmol/L] than in the SVR group (1363 nmol/L, IQR: 472 nmol/L, P < 0.001), as was that of high-density lipoprotein (HDL) particles (14168 nmol/L vs 15054 nmol/L, IQR: 4114 nmol/L vs 3385 nmol/L, P = 0.042). The number of very low-density lipoprotein (VLDL) particles was similar between the two groups. Among the four LDL sub-fractions, the number of large LDL particles was similar between the two groups. However, the numbers of medium (median: 533.0 nmol/L, IQR: 214.7 nmol/L vs median: 633.5 nmol/L, IQR: 229.6 nmol/L, P < 0.001), small (median: 190.9 nmol/L, IQR: 152.4 nmol/L vs median: 263.2 nmol/L, IQR: 159.9 nmol/L; P < 0.001), and very small LDL particles (median: 103.5 nmol/L, IQR: 66.8 nmol/L vs median: 139.3 nmol/L, IQR: 67.3 nmol/L, P < 0.001) were significantly lower in the active HCV group than in the SVR group, respectively. Multiple linear regression analysis indicated an association between HCV G1b infection and the decreased numbers of medium, small, and very small LDL particles. However, active HCV infection did not affect the number of large LDL particles or any sub-fractions of VLDL and HDL particles.

CONCLUSION: HCV G1b infection decreases the numbers of medium, small, and very small LDL particles.

Role of Conserved E2 Residue W420 in Receptor Binding and Hepatitis C Virus Infection

Hepatitis C virus (HCV) enters cells via interactions with several host factors, a key one being that between the viral E2 envelope glycoprotein and the CD81 receptor. We previously identified E2 tryptophan residue 420 (W420) as an essential CD81-binding residue. However, the importance of W420 in the context of the native virion is unknown, as those previous studies predate the infectious HCV cell culture (cell culture-derived HCV [HCVcc]) system. Here, we introduced four separate mutations (F, Y, A, or R) at position 420 within the infectious HCVcc JFH-1 genome and characterized their effects on the viral life cycle. While all mutations reduced E2-CD81 binding, only two (W420A and W420R) reduced HCVcc infectivity. Further analyses of mutants with hydrophobic residues (F or Y) found that interactions with the receptors SR-BI and CD81 were modulated, which in turn determined the viral uptake route. Both mutant viruses were significantly less dependent on SR-BI, and its lipid transfer activity, for virus entry. Furthermore, these viruses were resistant to the drug erlotinib, which targets epidermal growth factor receptor (EGFR) (a host cofactor for HCV entry) and also blocks SR-BI-dependent high-density lipoprotein (HDL)-mediated enhancement of virus entry. Together, our data indicate a model where an alteration at position 420 causes a subtle change in the E2 conformation that prevents interaction with SR-BI and increases accessibility to the CD81-binding site, in turn favoring a particular internalization route. These results further show that a hydrophobic residue with a strong preference for tryptophan at position 420 is important, both functionally and structurally, to provide an additional hydrophobic anchor to stabilize the E2-CD81 interaction.

IMPORTANCE

Hepatitis C virus (HCV) is a leading cause of liver disease, causing up to 500,000 deaths annually. The first step in the viral life cycle is the entry process. This study investigates the role of a highly conserved residue, tryptophan residue 420, of the viral glycoprotein E2 in this process. We analyzed the effect of changing this residue in the virus and confirmed that this region is important for binding to the CD81 receptor. Furthermore, alteration of this residue modulated interactions with the SR-BI receptor, and changes to these key interactions were found to affect the virus internalization route involving the host cofactor EGFR. Our results also show that the nature of the amino acid at this position is important functionally and structurally to provide an anchor point to stabilize the E2-CD81 interaction.

Rh-Catalyzed reductive Mannich-type reaction and its application towards the synthesis of (±)-ezetimibe

An effective synthesis for syn-β-lactams was achieved using a Rh-catalyzed reductive Mannich-type reaction. A rhodium–hydride complex (Rh–H) derived from diethylzinc (Et₂Zn) and a Rh catalyst was used for the 1,4-reduction of an α,β-unsaturated ester to give a Reformatsky-type reagent, which in turn, reacted with an imine to give the syn-β-lactam. Additionally, the reaction was applied to the synthesis of (±)-ezetimibe, a potent β-lactamic cholesterol absorption inhibitor.

Micrococcin P1, a naturally occurring macrocyclic peptide inhibiting hepatitis C virus entry in a pan-genotypic manner

Hepatitis C virus (HCV) is considered a major public health concern worldwide. Despite recent advances in curing chronic hepatitis C, unmet medical needs still remain, especially due to the high economic burden of therapies. Accordingly, our study aimed to identify affordable novel HCV inhibitors by screening of natural product compound libraries. We identified micrococcin P1, a macrocyclic peptide antibiotic, inhibiting HCV entry in a pan-genotypic manner with an EC50 range of 0.1-0.5 μM. Micrococcin P1 interfered with HCV entry at an attachment step. Furthermore, micrococcin P1 efficiently inhibited HCV spread by blocking cell-free infection as well as cell-to-cell transmission, without affecting the secretion of infectious virions. Interestingly, the putative molecular target of micrococcin P1 is glycoprotein E2 (IIe-630-Thr), as revealed by selection for viral drug resistance. In addition, micrococcin P1 inhibited sofosbuvir-resistant HCV strains and showed synergy in combination with selected HCV drugs, suggesting an alternative treatment paradigm for patients. In conclusion, we identified micrococcin P1 as specifically inhibiting entry of all HCV genotypes and demonstrated that micrococcin P1 potentially could add value to therapies in combination with current HCV interventions.

Hepatitis C virus depends on E-cadherin as an entry factor and regulates its expression in epithelial-to-mesenchymal transition

Hepatitis C virus (HCV) enters the host cell through interactions with a cascade of cellular factors. Although significant progress has been made in understanding HCV entry, the precise mechanisms by which HCV exploits the receptor complex and host machinery to enter the cell remain unclear. This intricate process of viral entry likely depends on additional yet-to-be-defined cellular molecules. Recently, by applying integrative functional genomics approaches, we identified and interrogated distinct sets of host dependencies in the complete HCV life cycle. Viral entry assays using HCV pseudoparticles (HCVpps) of various genotypes uncovered multiple previously unappreciated host factors, including E-cadherin, that mediate HCV entry. E-cadherin silencing significantly inhibited HCV infection in Huh7.5.1 cells, HepG2/miR122/CD81 cells, and primary human hepatocytes at a postbinding entry step. Knockdown of E-cadherin, however, had no effect on HCV RNA replication or internal ribosomal entry site (IRES)-mediated translation. In addition, an E-cadherin monoclonal antibody effectively blocked HCV entry and infection in hepatocytes. Mechanistic studies demonstrated that E-cadherin is closely associated with claudin-1 (CLDN1) and occludin (OCLN) on the cell membrane. Depletion of E-cadherin drastically diminished the cell-surface distribution of these two tight junction proteins in various hepatic cell lines, indicating that E-cadherin plays an important regulatory role in CLDN1/OCLN localization on the cell surface. Furthermore, loss of E-cadherin expression in hepatocytes is associated with HCV-induced epithelial-to-mesenchymal transition (EMT), providing an important link between HCV infection and liver cancer. Our data indicate that a dynamic interplay among E-cadherin, tight junctions, and EMT exists and mediates an important function in HCV entry.

A Schisandra-Derived Compound Schizandronic Acid Inhibits Entry of Pan-HCV Genotypes into Human Hepatocytes

Despite recent progress in the development of hepatitis C virus (HCV) inhibitors, cost-effective antiviral drugs, especially among the patients receiving liver transplantations, are still awaited. Schisandra is a traditional medicinal herb used to treat a range of liver disorders including hepatitis for thousands of years in China. To isolate the bioactive compounds of schisandra for the treatment of HCV infection, we screened a schisandra-extracts library and identified a tetracyclic triterpenoid, schizandronic acid (SZA), as a novel HCV entry inhibitor. Our findings suggested that SZA potently inhibited pan-HCV genotype entry into hepatoma cells and primary human hepatocytes without interfering virus binding on cell surface or internalization. However, virion-cell fusion process was impaired in the presence of SZA, along with the increased host membrane fluidity. We also found that SZA inhibited the spread of HCV to the neighboring cells, and combinations of SZA with interferon or telaprevir resulted in additive synergistic effect against HCV. Additionally, SZA diminished the establishment of HCV infection in vivo. The SZA target is different from conventional direct-acting antiviral agents, therefore, SZA is a potential therapeutic compound for the development of effective HCV entry inhibitors, especially for patients who need to prevent HCV reinfection during the course of liver transplantations.

New perspectives for preventing hepatitis C virus liver graft infection

Hepatitis C virus (HCV) infection is a leading cause of end-stage liver disease that necessitates liver transplantation. The incidence of virus-induced cirrhosis and hepatocellular carcinoma continues to increase, making liver transplantation increasingly common. Infection of the engrafted liver is universal and accelerates progression to advanced liver disease, with 20-30% of patients having cirrhosis within 5 years of transplantation. Treatments of chronic HCV infection have improved dramatically, albeit with remaining challenges of failure and access, and therapeutic options to prevent graft infection during liver transplantation are emerging. Developments in directed use of new direct-acting antiviral agents (DAAs) to eliminate circulating HCV before or after transplantation in the past 5 years provide renewed hope for prevention and treatment of liver graft infection. Identification of the ideal regimen and use of DAAs reveals new ways to treat this specific population of patients. Complementing DAAs, viral entry inhibitors have been shown to prevent liver graft infection in animal models and delay graft infection in clinical trials, which shows their potential for use concomitant to transplantation. We review the challenges and pathology associated with HCV liver graft infection, highlight current and future strategies of DAA treatment timing, and discuss the potential role of entry inhibitors that might be used synergistically with DAAs to prevent or treat graft infection.

Lipoprotein Receptors Redundantly Participate in Entry of Hepatitis C Virus

Scavenger receptor class B type 1 (SR-B1) and low-density lipoprotein receptor (LDLR) are known to be involved in entry of hepatitis C virus (HCV), but their precise roles and their interplay are not fully understood. In this study, deficiency of both SR-B1 and LDLR in Huh7 cells was shown to impair the entry of HCV more strongly than deficiency of either SR-B1 or LDLR alone. In addition, exogenous expression of not only SR-B1 and LDLR but also very low-density lipoprotein receptor (VLDLR) rescued HCV entry in the SR-B1 and LDLR double-knockout cells, suggesting that VLDLR has similar roles in HCV entry. VLDLR is a lipoprotein receptor, but the level of its hepatic expression was lower than those of SR-B1 and LDLR. Moreover, expression of mutant lipoprotein receptors incapable of binding to or uptake of lipid resulted in no or slight enhancement of HCV entry in the double-knockout cells, suggesting that binding and/or uptake activities of lipid by lipoprotein receptors are essential for HCV entry. In addition, rescue of infectivity in the double-knockout cells by the expression of the lipoprotein receptors was not observed following infection with pseudotype particles bearing HCV envelope proteins produced in non-hepatic cells, suggesting that lipoproteins associated with HCV particles participate in the entry through their interaction with lipoprotein receptors. Buoyant density gradient analysis revealed that HCV utilizes these lipoprotein receptors in a manner dependent on the lipoproteins associated with HCV particles. Collectively, these results suggest that lipoprotein receptors redundantly participate in the entry of HCV.

Hepatitis C virus (HCV) utilizes several receptors to enter hepatocytes, including scavenger receptor class B type 1 (SR-B1) receptor and low-density lipoprotein receptor (LDLR). HCV particles interact with lipoprotein and apolipoproteins to form complexes termed lipoviroparticles. Several reports have shown that SR-B1 and LDLR participate in the entry of lipoviroparticles through interaction with lipoproteins. However, the precise roles of SR-B1 and LDLR in HCV entry have not been fully clarified. In this study, we showed that SR-B1 and LDLR have a redundant role in HCV entry. In addition, we showed that very low-density lipoprotein receptor (VLDLR) played a role in HCV entry similar to the roles of SR-B1 and LDLR. Interestingly, VLDLR expression was low in the liver in contrast to the abundant expressions of SR-B1 and LDLR, but high in several extrahepatic tissues. Our data suggest that lipoprotein receptors participate in the entry of HCV particles associated with various lipoproteins.

Coadministration of ezetimibe with pegylated interferon plus ribavirin could improve early virological response in chronic hepatitis C obese Egyptian patients

BACKGROUND

Ezetimibe has been reported to inhibit viral entry and to reduce BMI and has been proposed as a novel therapeutic agent for chronic hepatitis C (CHC), potentiating the effects of pegylated interferon and ribavirin (peg-IFN/RBV).

OBJECTIVE

The aim of the study was to assess the effects of ezetimibe coadministration with peg-IFN/RBV combination on the early virological response (EVR) rates in nonobese and obese patients with CHC genotype 4 (CHC-4).

PATIENTS AND METHODS

A total of 144 CHC-4 patients were divided into two groups; group 1 included nonobese patients (n=76) and group 2 included obese patients (n=68). Each group was further subclassified into equal control and treated groups. The control groups received peg-IFN/RBV combination for 24 weeks, and the treated groups received peg-IFN/RBV plus ezetimibe for 12 weeks and then only peg-IFN/RBV for the remaining 12 weeks.

RESULTS

The study revealed that EVR significantly improved in the obese patients (85.3 vs. 64.7% in the treated and control groups, respectively, at P<0.05) without any significant improvement in the nonobese patients. Biochemical responses (defined as normalization of alanine aminotransferase at week 12) were markedly improved in the treated groups in both the nonobese and obese groups compared with their respective controls.

CONCLUSION

The addition of ezetimibe to peg-IFN/RBV combination significantly improves EVR rates in obese patients compared with nonobese patients, and remarkably improves the biochemical responses in both obese and nonobese patients with CHC-4. This may shed light on a new strategy for the treatment of CHC, particularly in obese Egyptian patients.

Identification of a Potent and Broad-Spectrum Hepatitis C Virus Fusion Inhibitory Peptide from the E2 Stem Domain

Hepatitis C virus (HCV) envelope proteins E1 and E2 play an essential role in virus entry. However, the fusion mechanisms of HCV remain largely unclear, hampering the development of efficient fusion inhibitors. Here, we developed two cell-based membrane fusion models that allow for screening a peptide library covering the full-length E1 and E2 amino acid sequences. A peptide from the E2 stem domain, named E27, was found to possess the ability to block E1E2-mediated cell-cell fusion and inhibit cell entry of HCV pseudoparticles and infection of cell culture-derived HCV at nanomolar concentrations. E27 demonstrated broad-spectrum inhibition of the major genotypes 1 to 6. A time-of-addition experiment revealed that E27 predominantly functions in the late steps during HCV entry, without influencing the expression and localization of HCV co-receptors. Moreover, we demonstrated that E27 interfered with hetero-dimerization of ectopically expressed E1E2 in cells, and mutational analysis suggested that E27 might target a conserved region in E1. Taken together, our findings provide a novel candidate as well as a strategy for developing potent and broad-spectrum HCV fusion inhibitors, which may complement the current direct-acting antiviral medications for chronic hepatitis C, and shed light on the mechanism of HCV membrane fusion.

ABHD5/CGI-58, the Chanarin-Dorfman Syndrome Protein, Mobilises Lipid Stores for Hepatitis C Virus Production

Hepatitis C virus (HCV) particles closely mimic human very-low-density lipoproteins (VLDL) to evade humoral immunity and to facilitate cell entry. However, the principles that govern HCV association with VLDL components are poorly defined. Using an siRNA screen, we identified ABHD5 (α/β hydrolase domain containing protein 5, also known as CGI-58) as a new host factor promoting both virus assembly and release. ABHD5 associated with lipid droplets and triggered their hydrolysis. Importantly, ABHD5 Chanarin-Dorfman syndrome mutants responsible for a rare lipid storage disorder in humans were mislocalised, and unable to consume lipid droplets or support HCV production. Additional ABHD5 mutagenesis revealed a novel tribasic motif that does not influence subcellular localization but determines both ABHD5 lipolytic and proviral properties. These results indicate that HCV taps into the lipid droplet triglyceride reservoir usurping ABHD5 lipase cofactor function. They also suggest that the resulting lipid flux, normally devoted to VLDL synthesis, also participates in the assembly and release of the HCV lipo-viro-particle. Altogether, our study provides the first association between the Chanarin-Dorfman syndrome protein and an infectious disease and sheds light on the hepatic manifestations of this rare genetic disorder as well as on HCV morphogenesis.

HCV replication is linked to the host lipid metabolism, and virions are secreted as lipo-viro-particles whose density, size and biochemical content resemble VLDL. HCV assembles close to lipid droplets and is released via the secretory pathway, but it remains unclear how it accesses the VLDL assembly pathway. In this study, we identified ABHD5 as a new host factor supporting HCV assembly and release. ABHD5 is a lipid droplet-associated lipase cofactor. In hepatocytes, ABHD5 was proposed to promote the recruitment of triglycerides from cytosolic towards luminal lipid droplets by mediating a cycle of phospholipid hydrolysis/re-esterification. Our data suggest that this ABHD5-dependent lipid transfer is not only required for VLDL maturation, but also for HCV assembly and virion release, indicating that lipid remodelling impacts on both assembly and virus transport. Finally, ABHD5 is associated with the Chanarin-Dorfman syndrome, a rare human genetic lipid metabolism disorder. We found that the Chanarin-Dorfman syndrome mutants were unable to support HCV assembly, pointing at a new host polymorphism that could determine susceptibility to HCV infection. Altogether, our results establish a new link between HCV, VLDL assembly and lipid remodeling pathways and open new possibilities to study the etiology of the liver manifestations of the Chanarin-Dorfman syndrome.

Roles of Lipoproteins and Apolipoproteins in Particle Formation of Hepatitis C Virus

More than 160 million people worldwide are infected with hepatitis C virus (HCV), and cirrhosis and hepatocellular carcinoma induced by HCV infection are life-threatening diseases. HCV takes advantage of many aspects of lipid metabolism for an efficient propagation in hepatocytes. Due to the morphological and physiological similarities of HCV particles to lipoproteins, lipid-associated HCV particles are named lipoviroparticles. Recent analyses have revealed that exchangeable apolipoproteins directly interact with the viral membrane to generate infectious HCV particles. In this review, we summarize the roles of lipid metabolism in the life cycle of HCV.

Hepatitis C Virus-Induced Degradation of Cell Death-Inducing DFFA-Like Effector B Leads to Hepatic Lipid Dysregulation

Individuals chronically infected with hepatitis C virus (HCV) commonly exhibit hepatic intracellular lipid accumulation, termed steatosis. HCV infection perturbs host lipid metabolism through both cellular and virus-induced mechanisms, with the viral core protein playing an important role in steatosis development. We have recently identified a liver protein, the cell death-inducing DFFA-like effector B (CIDEB), as an HCV entry host dependence factor that is downregulated by HCV infection in a cell culture model. In this study, we investigated the biological significance and molecular mechanism of this downregulation. HCV infection in a mouse model downregulated CIDEB in the liver tissue, and knockout of the CIDEB gene in a hepatoma cell line results in multiple aspects of lipid dysregulation that can contribute to hepatic steatosis, including reduced triglyceride secretion, lower lipidation of very-low-density lipoproteins, and increased lipid droplet (LD) stability. The potential link between CIDEB downregulation and steatosis is further supported by the requirement of the HCV core and its LD localization for CIDEB downregulation, which utilize a proteolytic cleavage event that is independent of the cellular proteasomal degradation of CIDEB.

IMPORTANCE

Our data demonstrate that HCV infection of human hepatocytesin vitroandin vivoresults in CIDEB downregulation via a proteolytic cleavage event. Reduction of CIDEB protein levels by HCV or gene editing, in turn, leads to multiple aspects of lipid dysregulation, including LD stabilization. Consequently, CIDEB downregulation may contribute to HCV-induced hepatic steatosis.

Activity-based and fraction-guided analysis of Phyllanthus urinaria identifies loliolide as a potent inhibitor of hepatitis C virus entry

Without a vaccine, hepatitis C virus (HCV) remains a global medical and socio-economic burden, predisposing about 170 million carriers worldwide to end-stage liver diseases including cirrhosis and hepatocellular carcinoma. Although the recently developed direct-acting antivirals (DAAs) have revolutionized hepatitis C treatment, most of them are unsuitable for monotherapy due to risks of resistance, thus necessitating combination with interferon (IFN)-alpha, ribavirin, or additional DAAs. More importantly, the high cost associated with the DAAs restricts their accessibility to most parts of the world. Developing novel cost-effective anti-HCV therapeutics may help expand the scope of antivirals and treatment strategies against hepatitis C. Herein, we applied an activity-based and fraction-guided analysis of extracts from the medicinal plant Phyllanthus urinaria (P. urinaria), which yielded fraction 13 (F13) as possessing the most potent inhibitory activity against early viral entry of cell-culture HCV infection. Chemical analysis (silica gel chromatography followed by ESI LC-MS plus (1)H and (13)C NMR) of F13 identified loliolide (LOD), a monoterpenoid lactone, as a novel inhibitor of HCV entry. Specifically, LOD could efficiently inactivate HCV free virus particles, abrogate viral attachment, and impede viral entry/fusion, with minimal effect on viral replication/translation, particle production, and induction of type I IFN host antiviral immune response. ELISA-based binding analysis confirmed the monoterpenoid's ability in efficiently blocking HCV particle attachment to the host cell surface. Furthermore, LOD could inhibit infection by several genotypic strains of HCV. This is the first report characterizing P. urinaria and its bioactive compound LOD as potent HCV entry inhibitors, which merit further evaluation for development as candidate antiviral agents against hepatitis C.

CD36 is a co-receptor for hepatitis C virus E1 protein attachment

The cluster of differentiation 36 (CD36) is a membrane protein related to lipid metabolism. We show that HCV infection in vitro increased CD36 expression in either surface or soluble form. HCV attachment was facilitated through a direct interaction between CD36 and HCV E1 protein, causing enhanced entry and replication. The HCV co-receptor effect of CD36 was independent of that of SR-BI. CD36 monoclonal antibodies neutralized the effect of CD36 and reduced HCV replication. CD36 inhibitor sulfo-N-succinimidyl oleate (SSO), which directly bound CD36 but not SR-BI, significantly interrupted HCV entry, and therefore inhibited HCV replication. SSO’s antiviral effect was seen only in HCV but not in other viruses. SSO in combination with known anti-HCV drugs showed additional inhibition against HCV. SSO was considerably safe in mice. Conclusively, CD36 interacts with HCV E1 and might be a co-receptor specific for HCV entry; thus, CD36 could be a potential drug target against HCV.

Sphingolipids in viral infection

Viruses exploit membranes and their components such as sphingolipids in all steps of their life cycle including attachment and membrane fusion, intracellular transport, replication, protein sorting and budding. Examples for sphingolipid-dependent virus entry are found for: human immunodeficiency virus (HIV), which besides its protein receptors also interacts with glycosphingolipids (GSLs); rhinovirus, which promotes the formation of ceramide-enriched platforms and endocytosis; or measles virus (MV), which induces the surface expression of its own receptor CD150 via activation of sphingomyelinases (SMases). While SMase activation was implicated in Ebola virus (EBOV) attachment, the virus utilizes the cholesterol transporter Niemann-Pick C protein 1 (NPC1) as 'intracellular' entry receptor after uptake into endosomes. Differential activities of SMases also affect the intracellular milieu required for virus replication. Sindbis virus (SINV), for example, replicates better in cells lacking acid SMase (ASMase). Defined lipid compositions of viral assembly and budding sites influence virus release and infectivity, as found for hepatitis C virus (HCV) or HIV. And finally, viruses manipulate cellular signaling and the sphingolipid metabolism to their advantage, as for example influenza A virus (IAV), which activates sphingosine kinase 1 and the transcription factor NF-κB.

Recent advances in understanding hepatitis C

The past decade has seen tremendous progress in understanding hepatitis C virus (HCV) biology and its related disease, hepatitis C. Major advances in characterizing viral replication have led to the development of direct-acting anti-viral therapies that have considerably improved patient treatment outcome and can even cure chronic infection. However, the high cost of these treatments, their low barrier to viral resistance, and their inability to prevent HCV-induced liver cancer, along with the absence of an effective HCV vaccine, all underscore the need for continued efforts to understand the biology of this virus. Moreover, beyond informing therapies, enhanced knowledge of HCV biology is itself extremely valuable for understanding the biology of related viruses, such as dengue virus, which is becoming a growing global health concern. Major advances have been realized over the last few years in HCV biology and pathogenesis, such as the discovery of the envelope glycoprotein E2 core structure, the generation of the first mouse model with inheritable susceptibility to HCV, and the characterization of virus-host interactions that regulate viral replication or innate immunity. Here, we review the recent findings that have significantly advanced our understanding of HCV and highlight the major challenges that remain.

Discovery, Optimization, and Characterization of Novel Chlorcyclizine Derivatives for the Treatment of Hepatitis C Virus Infection

Recently, we reported that chlorcyclizine (CCZ, Rac-2), an over-the-counter antihistamine piperazine drug, possesses in vitro and in vivo activity against hepatitis C virus. Here, we describe structure-activity relationship (SAR) efforts that resulted in the optimization of novel chlorcyclizine derivatives as anti-HCV agents. Several compounds exhibited EC50 values below 10 nM against HCV infection, cytotoxicity selectivity indices above 2000, and showed improved in vivo pharmacokinetic properties. The optimized molecules can serve as lead preclinical candidates for the treatment of hepatitis C virus infection and as probes to study hepatitis C virus pathogenesis and host-virus interaction.

Host restriction factors for hepatitis C virus

Host-hepatitis C virus (HCV) interactions have both informed fundamental concepts of viral replication and pathogenesis and provided novel insights into host cell biology. These findings are illustrated by the recent discovery of host-encoded factors that restrict HCV infection. In this review, we briefly discuss these restriction factors in different steps of HCV infection. In each case, we discuss how these restriction factors were identified, the mechanisms by which they inhibit HCV infection and their potential contribution to viral pathogenesis.

Comparative Proteomics Reveals Important Viral-Host Interactions in HCV-Infected Human Liver Cells

Hepatitis C virus (HCV) poses a global threat to public health. HCV envelop protein E2 is the major component on the virus envelope, which plays an important role in virus entry and morphogenesis. Here, for the first time, we affinity purified E2 complex formed in HCV-infected human hepatoma cells and conducted comparative mass spectrometric analyses. 85 cellular proteins and three viral proteins were successfully identified in three independent trials, among which alphafetoprotein (AFP), UDP-glucose: glycoprotein glucosyltransferase 1 (UGT1) and HCV NS4B were further validated as novel E2 binding partners. Subsequent functional characterization demonstrated that gene silencing of UGT1 in human hepatoma cell line Huh7.5.1 markedly decreased the production of infectious HCV, indicating a regulatory role of UGT1 in viral lifecycle. Domain mapping experiments showed that HCV E2-NS4B interaction requires the transmembrane domains of the two proteins. Altogether, our proteomics study has uncovered key viral and cellular factors that interact with E2 and provided new insights into our understanding of HCV infection.

Entry inhibitors: New advances in HCV treatment

Hepatitis C virus (HCV) infection affects approximately 3% of the world's population and causes chronic liver diseases, including liver fibrosis, cirrhosis, and hepatocellular carcinoma. Although current antiviral therapy comprising direct-acting antivirals (DAAs) can achieve a quite satisfying sustained virological response (SVR) rate, it is still limited by viral resistance, long treatment duration, combined adverse reactions, and high costs. Moreover, the currently marketed antivirals fail to prevent graft reinfections in HCV patients who receive liver transplantations, probably due to the cell-to-cell transmission of the virus, which is also one of the main reasons behind treatment failure. HCV entry is a highly orchestrated process involving initial attachment and binding, post-binding interactions with host cell factors, internalization, and fusion between the virion and the host cell membrane. Together, these processes provide multiple novel and promising targets for antiviral therapy. Most entry inhibitors target host cell components with high genetic barriers and eliminate viral infection from the very beginning of the viral life cycle. In future, the addition of entry inhibitors to a combination of treatment regimens might optimize and widen the prevention and treatment of HCV infection. This review summarizes the molecular mechanisms and prospects of the current preclinical and clinical development of antiviral agents targeting HCV entry.

The Synthetic Antiviral Drug Arbidol Inhibits Globally Prevalent Pathogenic Viruses

Arbidol (ARB) is a synthetic antiviral originally developed to combat influenza viruses. ARB is currently used clinically in several countries but not in North America. We have previously shown that ARB inhibits in vitro hepatitis C virus (HCV) by blocking HCV entry and replication. In this report, we expand the list of viruses that are inhibited by ARB and demonstrate that ARB suppresses in vitro infection of mammalian cells with Ebola virus (EBOV), Tacaribe arenavirus, and human herpesvirus 8 (HHV-8). We also confirm suppression of hepatitis B virus and poliovirus by ARB. ARB inhibited EBOV Zaire Kikwit infection when added before or at the same time as virus infection and was less effective when added 24 h after EBOV infection. Experiments with recombinant vesicular stomatitis virus (VSV) expressing the EBOV Zaire glycoprotein showed that infection was inhibited by ARB at early stages, most likely at the level of viral entry into host cells. ARB inhibited HHV-8 replication to a similar degree as cidofovir. Our data broaden the spectrum of antiviral efficacy of ARB to include globally prevalent viruses that cause significant morbidity and mortality.

IMPORTANCE

There are many globally prevalent viruses for which there are no licensed vaccines or antiviral medicines. Some of these viruses, such as Ebola virus or members of the arenavirus family, rapidly cause severe hemorrhagic diseases that can be fatal. Other viruses, such as hepatitis B virus or human herpesvirus 8 (HHV-8), establish persistent infections that cause chronic illnesses, including cancer. Thus, finding an affordable, effective, and safe drug that blocks many viruses remains an unmet medical need. The antiviral drug arbidol (ARB), already in clinical use in several countries as an anti-influenza treatment, has been previously shown to suppress the growth of many viruses. In this report, we expand the list of viruses that are blocked by ARB in a laboratory setting to include Ebola virus, Tacaribe arenavirus, and HHV-8, and we propose ARB as a broad-spectrum antiviral drug that may be useful against hemorrhagic viruses.

Repurposing of the antihistamine chlorcyclizine and related compounds for treatment of hepatitis C virus infection

Hepatitis C virus (HCV) infection affects an estimated 185 million people worldwide, with chronic infection often leading to liver cirrhosis and hepatocellular carcinoma. Although HCV is curable, there is an unmet need for the development of effective and affordable treatment options. Through a cell-based high-throughput screen, we identified chlorcyclizine HCl (CCZ), an over-the-counter drug for allergy symptoms, as a potent inhibitor of HCV infection. CCZ inhibited HCV infection in human hepatoma cells and primary human hepatocytes. The mode of action of CCZ is mediated by inhibiting an early stage of HCV infection, probably targeting viral entry into host cells. The in vitro antiviral effect of CCZ was synergistic with other anti-HCV drugs, including ribavirin, interferon-α, telaprevir, boceprevir, sofosbuvir, daclatasvir, and cyclosporin A, without significant cytotoxicity, suggesting its potential in combination therapy of hepatitis C. In the mouse pharmacokinetic model, CCZ showed preferential liver distribution. In chimeric mice engrafted with primary human hepatocytes, CCZ significantly inhibited infection of HCV genotypes 1b and 2a, without evidence of emergence of drug resistance, during 4 and 6 weeks of treatment, respectively. With its established clinical safety profile as an allergy medication, affordability, and a simple chemical structure for optimization, CCZ represents a promising candidate for drug repurposing and further development as an effective and accessible agent for treatment of HCV infection.

Flunarizine prevents hepatitis C virus membrane fusion in a genotype-dependent manner by targeting the potential fusion peptide within E1

To explore mechanisms of hepatitis C viral (HCV) replication we screened a compound library including licensed drugs. Flunarizine, a diphenylmethylpiperazine used to treat migraine, inhibited HCV cell entry in vitro and in vivo in a genotype-dependent fashion. Analysis of mosaic viruses between susceptible and resistant strains revealed that E1 and E2 glycoproteins confer susceptibility to flunarizine. Time of addition experiments and single particle tracking of HCV demonstrated that flunarizine specifically prevents membrane fusion. Related phenothiazines and pimozide also inhibited HCV infection and preferentially targeted HCV genotype 2 viruses. However, phenothiazines and pimozide exhibited improved genotype coverage including the difficult to treat genotype 3. Flunarizine-resistant HCV carried mutations within the alleged fusion peptide and displayed cross-resistance to these compounds, indicating that these drugs have a common mode of action.

CONCLUSION

These observations reveal novel details about HCV membrane fusion; moreover, flunarizine and related compounds represent first-in-class HCV fusion inhibitors that merit consideration for repurposing as a cost-effective component of HCV combination therapies.

The role of cellular adhesion molecules in virus attachment and entry

As obligate intracellular parasites, viruses must traverse the host-cell plasma membrane to initiate infection. This presents a formidable barrier, which they have evolved diverse strategies to overcome. Common to all entry pathways, however, is a mechanism of specific attachment to cell-surface macromolecules or ‘receptors’. Receptor usage frequently defines viral tropism, and consequently, the evolutionary changes in receptor specificity can lead to emergence of new strains exhibiting altered pathogenicity or host range. Several classes of molecules are exploited as receptors by diverse groups of viruses, including, for example, sialic acid moieties and integrins. In particular, many cell-adhesion molecules that belong to the immunoglobulin-like superfamily of proteins (IgSF CAMs) have been identified as viral receptors. Structural analysis of the interactions between viruses and IgSF CAM receptors has not shown binding to specific features, implying that the Ig-like fold may not be key. Both proteinaceous and enveloped viruses exploit these proteins, however, suggesting convergent evolution of this trait. Their use is surprising given the usually occluded position of CAMs on the cell surface, such as at tight junctions. Nonetheless, the reason for their widespread involvement in virus entry most probably originates in their functional rather than structural characteristics.

Hepatitis C virus utilizes VLDLR as a novel entry pathway

Various host factors are involved in the cellular entry of hepatitis C virus (HCV). In addition to the factors previously reported, we discovered that the very-low-density lipoprotein receptor (VLDLR) mediates HCV entry independent of CD81. Culturing Huh7.5 cells under hypoxic conditions significantly increased HCV entry as a result of the expression of VLDLR, which was not expressed under normoxic conditions in this cell line. Ectopic VLDLR expression conferred susceptibility to HCV entry of CD81-deficient Huh7.5 cells. Additionally, VLDLR-mediated HCV entry was not affected by the knockdown of cellular factors known to act as HCV receptors or HCV entry factors. Because VLDLR is expressed in primary human hepatocytes, our results suggest that VLDLR functions in vivo as an HCV receptor independent of canonical CD81-mediated HCV entry.