Hepatitis C virus-biology, host evasion strategies, and promising new therapies on the horizon

Prevalence of Hepatitis B and Hepatitis C Viral Infections and Their Associated Factors among Diabetic Patients Visiting Debre Tabor Referral Hospital, Northwest Ethiopia, 2021: A Cross-Sectional Study

Background

Viral hepatitis is a global public health problem that affects millions of people each year, causing disability and death. Hepatitis B and C viruses are the most common causes of viral hepatitis and are associated with chronic liver disease, cirrhosis, and hepatocellular carcinoma. The primary site of infection for these viruses is the liver, the primary site of hormone and glucose metabolism closely linked to diabetes mellitus (DM), which is associated with increased morbidity and mortality worldwide. As a result, assessing the coexistence of viral hepatitis and DM could be important in disease management, prevention, and control measures in DM patients.

Objective

The aim of our study is to assess the prevalence and associated factors of HBV and HCV among diabetes patients attending Debre Tabor Referral Hospital.

Methods

An institutional-based, cross-sectional study was conducted from December 1, 2021, to February 30, 2021. A systematic sampling technique was used for selecting study participants. Serum samples were screened with a rapid test kit for hepatitis B (HBV) and hepatitis C (HCV) infections. A pretested structured questionnaire was constructed to collect the data, which were later analyzed using SPSS version 23. Inferential statistics were used to evaluate the associated risk factors for the outcome variable. A p value of <0.05 was considered statistically significant.

Result

A total of 152 diabetes patients were included in this study, with 78 (51.3%) males and 74 (48.7%) females, with a mean age of 39.24 ± 17.90 years. The prevalence of HBV and HCV was 6 (3.9%) and 2 (1.3%), respectively. Most of potential risk factors such as, histories of surgical procedures, tooth extraction, hepatitis infection in the family, blood transfusion, alcohol consumption, body tattooing, and multiple sexual partners were not statistically significant for HBV and HCV infections.

Conclusion

In this study, no association was obtained between sociodemographic, clinical, and behavioural factors and the prevalence of hepatitis B and C viruses. Furthermore, there is no significant association detected between HBV or potential HCV infection and DM. Despite these results, continuing professional training programs on HBV and HCV infection, including increased vaccination coverage rates for HBV, are required.

Sulfur(vi) fluoride exchange as a key reaction for synthesizing biaryl sulfate core derivatives as potent hepatitis C virus NS5A inhibitors and their structure-activity relationship studies

Extremely potent, new hepatitis C virus (HCV) nonstructural 5A (NS5A) featuring substituted biaryl sulfate core structures was designed and synthesized. Based on the previously reported novel HCV NS5A inhibitors featuring biaryl sulfate core structures which exhibit two-digit picomolar half-maximal effective concentration (EC50) values against HCV genotype 1b and 2a, the new inhibitors equipped with the sulfate core structures containing diversely substituted aryl groups were explored. In this study, highly efficient, chemoselective coupling reactions between an arylsulfonyl fluoride and an aryl silyl ether, known as the sulfur(vi) fluoride exchange (SuFEx) reaction, were utilized. Among the inhibitors prepared based on the SuFEx chemistry, compounds 14, 15 and 29 exhibited two-digit picomolar EC50 values against GT-1b and single digit or sub nanomolar activities against the HCV GT-2a strain. Nonsymmetrical inhibitors containing an imidazole and amide moieties on each side of the sulfate core structures were also synthesized. In addition, a biotinylated probe targeting NS5A protein was prepared for labeling using the same synthetic methodology.

New potent biaryl sulfate-based hepatitis C virus inhibitors

The discovery of a new series of potent hepatitis C virus (HCV) NS5A inhibitors containing biaryl sulfone or sulfate cores is reported. Structure-activity relationship (SAR) studies on inhibitors containing various substitution patterns of the sulfate or sulfone core structure established that m-,m'- substituted biaryl sulfate core-based inhibitors containing an amide moiety (compound 20) or an imidazole moiety (compound 24) showed extremely high potency. Compound 20 demonstrated double-digit pM potencies against both genotype 1b (GT-1b) and 2a (GT-2a). Compound 24 also exhibited double-digit pM potencies against GT-1b and sub nM potencies against GT-2a. Furthermore, compounds 20 and 24 exhibited no cardiotoxicity in an hERG ligand binding assay and showed acceptable plasma stability and no mutagenic potential in the Ames test. In addition, these compounds showed distinctive additive effects in combination treatment with the NS5B targeting drug sofosbuvir (Sovaldi^®). The results of this study showed that the compounds 20 and 24 could be effective HCV inhibitors.

Novel benzidine and diaminofluorene prolinamide derivatives as potent hepatitis C virus NS5A inhibitors

Our study describes the discovery of a series of highly potent hepatitis C virus (HCV) NS5A inhibitors based on symmetrical prolinamide derivatives of benzidine and diaminofluorene. Through modification of benzidine, l-proline, and diaminofluorene derivatives, we developed novel inhibitor structures, which allowed us to establish a library of potent HCV NS5A inhibitors. After optimizing the benzidine prolinamide backbone, we identified inhibitors embedding meta-substituted benzidine core structures that exhibited the most potent anti-HCV activities. Furthermore, through a battery of studies including hERG ligand binding assay, CYP450 binding assay, rat plasma stability test, human liver microsomal stability test, and pharmacokinetic studies, the identified compounds 24, 26, 27, 42, and 43 are found to be nontoxic, and are expected to be effective therapeutic anti-HCV agents.

Structure-function analysis of hepatitis C virus envelope glycoproteins E1 and E2

Hepatitis C virus (HCV) is the leading cause of chronic liver disease in humans. The envelope proteins of HCV are potential candidates for vaccine development. The absence of three-dimensional (3D) structures for the functional domain of HCV envelope proteins [E1.E2] monomer complex has hindered overall understanding of the virus infection, and also structure-based drug design initiatives. In this study, we report a 3D model containing both E1 and E2 proteins of HCV using the recently published structure of the core domain of HCV E2 and the functional part of E1, and investigate immunogenic implications of the model. HCV [E1.E2] molecule is modeled by using aa205-319 of E1 to aa421-716 of E2. Published experimental data were used to further refine the [E1.E2] model. Based on the model, we predict 77 exposed residues and several antigenic sites within the [E1.E2] that could serve as vaccine epitopes. This study identifies eight peptides which have antigenic propensity and have two or more sequentially exposed amino acids and 12 singular sites are under negative selection pressure that can serve as vaccine or therapeutic targets. Our special interest is 285FLVGQLFTFSPRRHW299 which has five negatively selected sites (L286, V287, G288, T292, and G303) with three of them sequential and four amino acids exposed (F285, L286, T292, and R296). This peptide in the E1 protein maps to dengue envelope vaccine target identified previously by our group. Our model provides for the first time an overall view of both the HCV envelope proteins thereby allowing researchers explore structure-based drug design approaches.

Discovery and development of hepatitis C virus NS5A replication complex inhibitors

Lead inhibitors that target the function of the hepatitis C virus (HCV) nonstructural 5A (NS5A) protein have been identified by phenotypic screening campaigns using HCV subgenomic replicons. The demonstration of antiviral activity in HCV-infected subjects by the HCV NS5A replication complex inhibitor (RCI) daclatasvir (1) spawned considerable interest in this mechanistic approach. In this Perspective, we summarize the medicinal chemistry studies that led to the discovery of 1 and other chemotypes for which resistance maps to the NS5A protein and provide synopses of the profiles of many of the compounds currently in clinical trials. We also summarize what is currently known about the NS5A protein and the studies using NS5A RCIs and labeled analogues that are helping to illuminate aspects of both protein function and inhibitor interaction. We conclude with a synopsis of the results of notable clinical trials with HCV NS5A RCIs.

Improving the Resistance Profile of Hepatitis C NS3/4A Inhibitors: Dynamic Substrate Envelope Guided Design

Drug resistance is a principal concern in the treatment of quickly evolving diseases. The viral protease NS3/4A is a primary drug target for the hepatitis C virus (HCV) and is known to evolve resistance mutations in response to drug therapy. At the molecular level, drug resistance reflects a subtle change in the balance of molecular recognition by NS3/4A; the drug resistant protease variants are no longer effectively inhibited by the competitive active site inhibitors but can still process the natural substrates with enough efficiency for viral survival. In previous works we have developed the "substrate envelope" hypothesis, which posits that inhibitors should be less susceptible to drug resistance if they better mimic the natural substrate molecular recognition features. In this work, we perform molecular dynamics simulations on four native substrates bound to NS3/4A and discover a clearly conserved dynamic substrate envelope. We show that the most severe drug resistance mutations in NS3/4A occur at residues that are outside the substrate envelope. Comparative analysis of three NS3/4A inhibitors reveals structural and dynamic characteristics of inhibitors that could lead to resistance. We also suggest inhibitor modifications to improve resistance profiles based on the dynamic substrate envelope. This study provides a general framework for guiding the development of novel inhibitors that will be more robust against resistance by mimicking the static and dynamic binding characteristics of natural substrates.

Structural modeling of HCV NS3/4A serine protease drug-resistance mutations using end-point continuum solvation and side-chain flexibility calculations

Computational methods of modeling protein-ligand interactions have gained widespread application in modern drug discovery. In continuum solvation-based methods of binding affinity estimation, limited description of solvent environment and protein flexibility is traded for a time scale that fits medicinal chemistry test cycles. The results of this speed-accuracy trade-off have been promising in terms of modeling structure-activity relationships of ligand series against protein targets. The potential of these approaches in recapitulating structural and energetic effects of resistance mutations, which involve large changes in binding affinity, remains relatively unexplored. We used continuum solvation binding affinity predictions and graph theory-based flexibility calculations to model thirteen drug resistance mutations in HCV NS3/4A serine protease, against three small-molecule inhibitors, with a 2-fold objective: quantitative assessment of binding energy predictions against experimental data and elucidation of structural/energetic determinants of resistance. The results show statistically significant correlation between predicted and experimental binding affinities, with R(2) and predictive index of up to 0.83 and 0.91, respectively. The level of accuracy was consistent with what has been reported for the inverse problem of binding affinity estimation of congeneric ligands against the same target. The quality of predictions was poor for mutations involving induced-fit effects, primarily, because of the lack of entropy terms. Flexibility analysis explained this discrepancy by indicating characteristic changes in side-chain mobility of a key binding site residue. The combined results from two approaches provide novel insights regarding the molecular mechanism of resistance. NS3/4A inhibitors, with large P2 substituents, derive high affinity with optimal van der Waals interactions in the S2 subsite, in order to overcome unfavorable desolvation and entropic cost of induced-fit effects. High-level resistance mutations tend to increase the desolvation and/or entropic barrier to ligand binding. The lead optimization strategies should, therefore, address the balance of these opposing energetic contributions in both the wild-type and mutant target.

A new class of pyrimidine nucleosides: inhibitors of hepatitis B and C viruses

Hepatitis B virus (HBV) and hepatitis C virus (HCV) infections are major health threats worldwide leading to liver cirrhosis, liver cancer and mortality. Herein, we report a new category of dideoxy pyrimidine nucleosides possessing a 4'-carboxyl (or carboxymethyl) function (7-9, 13, 16, 17), which are discovered as potential antiviral agents. For the first time, these nucleosides are recognized to be inhibitors of HBV and/or HCV replication. Among 4'-carboxy compounds, 3',4'-didehydrothymidine (16) was most effective against DHBV, HBV and HCV. Modification of the 4'-position in compound 7 from a carboxyl to carboxymethyl group (17) did not affect the anti-HBV activity but greatly increased the anti-HCV activity. Importantly, 17 yielded synergistic antiviral effect when combined with ribavirin without toxicity. The activity exhibited by a single agent towards both hepatitis viruses and no detectable in vitro cytotoxicity make this new class of compounds of interest.

Association of Hepatitis C Virus Infection with Type II Diabetes in Ethiopia: A Hospital-Based Case-Control Study

Background. Chronic hepatitis C virus (HCV) has become the global “epidemic” with an estimated 123 million people currently infected worldwide. As the same time diabetes is also rapidly emerging as a global health care problem that threatens to reach pandemic levels by 2030. Objective. To investigate the magnitude of HCV infection in type II diabetes as compared to controls. Methodology. A case control study design was conducted at Jimma University Specialized Hospital from May to June 2010. A total of 604 study subjects were included in this study. Sociodemographic and risk factor data were collected by questionnaire. From serum sample, HCVAb screening was done by rapid antibody screening test. Liver functioning tests and total cholesterol tests were done by Dr. Lange LP 800 spectrophotometer. Results. The prevalence of HCV in type II diabetes and nondiabetic controls was 9.9% and 3.3%, respectively. In multivariate analysis, HCV seropositives have high risk of developing diabetes as compared with seronegatives (AOR = 2.997, 95% CI: (1.08, 8.315)). Conclusion. In this study, we found a positive association between past HCV infection and type II diabetes. As we did not perform HCV RNA test, we could not assess the association with HCV viremia.

HIV-1 Protease and Substrate Coevolution Validates the Substrate Envelope As the Substrate Recognition Pattern

Drug resistance of HIV-1 protease alters the balance in the molecular recognition events in favor of substrate processing versus inhibitor binding. To develop robust inhibitors targeting ensembles of drug-resistant variants, the code of this balance needs to be cracked. For this purpose, the principles governing the substrate recognition are required to be revealed. Previous crystallographic studies on the WT protease-substrate complexes showed that the substrates have a conserved consensus volume in the protease active site despite their low sequence homology. This consensus volume is termed as the substrate envelope. The substrate envelope was recently reevaluated by taking the substrate dynamics into account, and the dynamic substrate envelope was reported to better define the substrate specificity for HIV-1 protease. Drug resistance occurs mostly through mutations in the protease, occasionally accompanied by cleavage site mutations. In this study, three coevolved protease-substrate complexes (^AP2VNC-p1_V82A, ^LP1'Fp1-p6_D30N/N88D, and ^SP3'Np1-p6_D30N/N88D) were investigated for structural and dynamic properties by molecular modeling and dynamics simulations. The results show the substrate envelope is preserved by these cleavage site mutations in the presence of drug-resistance mutations in the protease, if not enhanced. This study on the conformational and mutational ensembles of protease-substrate complexes validates the substrate envelope as the substrate recognition motif for HIV-1 protease. The substrate envelope hypothesis allows for the elucidation of possible drug resistance mutation patterns in the polyprotein cleavage sites.

Zebrafish as a potential model organism for drug test against hepatitis C virus

Screening and evaluating anti- hepatitis C virus (HCV) drugs in vivo is difficult worldwide, mainly because of the lack of suitable small animal models. We investigate whether zebrafish could be a model organism for HCV replication. To achieve NS5B-dependent replication an HCV sub-replicon was designed and created with two vectors, one with HCV ns5b and fluorescent rfp genes, and the other containing HCV's 5′UTR, core, 3′UTR and fluorescent gfp genes. The vectors containing sub-replicons were co-injected into zebrafish zygotes. The sub-replicon amplified in liver showing a significant expression of HCV core RNA and protein. The sub-replicon amplification caused no abnormality in development and growth of zebrafish larvae, but induced gene expression change similar to that in human hepatocytes. As the amplified core fluorescence in live zebrafish was detectable microscopically, it rendered us an advantage to select those with replicating sub-replicon for drug experiments. Ribavirin and oxymatrine, two known anti-HCV drugs, inhibited sub-replicon amplification in this model showing reduced levels of HCV core RNA and protein. Technically, this method had a good reproducibility and is easy to operate. Thus, zebrafish might be a model organism to host HCV, and this zebrafish/HCV (sub-replicon) system could be an animal model for anti-HCV drug screening and evaluation.

Drug resistance against HCV NS3/4A inhibitors is defined by the balance of substrate recognition versus inhibitor binding

Hepatitis C virus infects an estimated 180 million people worldwide, prompting enormous efforts to develop inhibitors targeting the essential NS3/4A protease. Resistance against the most promising protease inhibitors, telaprevir, boceprevir, and ITMN-191, has emerged in clinical trials. In this study, crystal structures of the NS3/4A protease domain reveal that viral substrates bind to the protease active site in a conserved manner defining a consensus volume, or substrate envelope. Mutations that confer the most severe resistance in the clinic occur where the inhibitors protrude from the substrate envelope, as these changes selectively weaken inhibitor binding without compromising the binding of substrates. These findings suggest a general model for predicting the susceptibility of protease inhibitors to resistance: drugs designed to fit within the substrate envelope will be less susceptible to resistance, as mutations affecting inhibitor binding would simultaneously interfere with the recognition of viral substrates.

A comparative QM/MM study of the reaction mechanism of the Hepatitis C virus NS3/NS4A protease with the three main natural substrates NS5A/5B, NS4B/5A and NS4A/4B

The reaction mechanism of the NS3/NS4A protease with the NS4B/5A and NS4A/4B natural substrates has been investigated using the QM/MM (quantum mechanics/molecular mechanics) approach, and some calculations have been performed on the reaction with the NS5A/5B natural substrate. This study widely extends a previous contribution of our group on the reaction mechanism with the NS5A/5B substrate, the main goal here being to understand the differences found between the reaction mechanism of each natural substrate and the role played by the enzymatic residues in the catalytic cycle. This knowledge will ultimately help in developing new NS3/NS4A protease inhibitors. The two first steps of the mechanism have been considered: Acylation and breaking of the peptide bond, with emphasis on the former one (rate limiting process). Energy and free energy profiles for both steps have been calculated at the AM1/MM level and corrected by means of MP2 ab initio calculations, being evident the importance of correlation energy. Acylation is the rate limiting step in all cases and occurs through a tetracoordinated intermediate, as previously suggested for other serine proteases. Specificities in the NS4B/5A mechanism can be attributed to the presence of a Proline residue in the substrate P2 position. The analysis of structures and energies confirm the importance of the oxyanion hole in the electrostatic stabilization of the tetracoordinated intermediate. Finally, the role of other residues, e.g., Arg-155 and Asp-79, has been explained, and the viability of Arg-155 mutants and its resistance to some protease inhibitors has been understood thanks to virtual mutation studies.

Hepatitis C virus genomic RNA dimerization is mediated via a kissing complex intermediate

With over 200 million people infected with hepatitis C virus (HCV) worldwide, there is a need for more effective and better-tolerated therapeutic strategies. The HCV genome is a positive-sense; single-stranded RNA encoding a large polyprotein cleaved at multiple sites to produce at least ten proteins, among them an error-prone RNA polymerase that confers a high mutation rate. Despite considerable overall sequence diversity, in the 3'-untranslated region of the HCV genomic RNA there is a 98-nucleotide (nt) sequence named X RNA, the first 55 nt of which (X55 RNA) are 100% conserved among all HCV strains. The X55 region has been suggested to be responsible for in vitro dimerization of the genomic RNA in the presence of the viral core protein, although the mechanism by which this occurs is unknown. In this study, we analyzed the X55 region and characterized the mechanism by which it mediates HCV genomic RNA dimerization. Similar to a mechanism proposed previously for the human immunodeficiency 1 virus (HIV-1) genome, we show that dimerization of the HCV genome involves formation of a kissing complex intermediate, which is converted to a more stable extended duplex conformation in the presence of the core protein. Mutations in the dimer linkage sequence loop sequence that prevent RNA dimerization in vitro significantly reduced but did not completely ablate the ability of HCV RNA to replicate or produce infectious virus in transfected cells.

HCV drug discovery aimed at viral eradication

Hepatitis C virus (HCV) causes significant morbidity and mortality worldwide with nearly 3% of the world population infected by this virus. Fortunately, this virus does not establish latency, and hence it may be possible to eradicate it. HCV is strongly associated with liver cirrhosis and hepatocellular carcinoma and is currently treated with pegylated interferon-alpha (peg-IFN-alpha) and ribavirin. Unfortunately, these limited treatment options often produce significant side effects, and currently, complete eradication of virus with combined drug modalities has not yet been achieved for the majority of chronically HCV-infected individuals. Restricted treatment options, lack of a universal cure for HCV and the link between chronic infection, liver cirrhosis and hepatocellular carcinoma necessitate design of novel drugs and treatment options. Understanding the relationship between the immune response, viral clearance and inhibition of viral replication with pharmacology-based design can ultimately allow for complete eradication of HCV. This review focuses upon significant novel preclinical and clinical specifically targeted antiviral therapy (STAT-C) drugs under development, highlights their mechanism of action, and discusses their impact on systemic viral loads and permanent clearance of infection.

Hepatitis C therapy--the future looks bright

Hepatitis C virus (HCV) infections affect about 170 million individuals worldwide and can be life-threatening if left untreated. Over the past three decades, ribavirin and interferon-alpha have remained the only available medicines for treating hepatitis C sufferers. Given that this combination therapy is partially effective at best and is associated with severe side-effects, there is an unmet need for new molecular entities which inhibit HCV replication. By employing a combination of structure-based drug design together with high-throughput screening approaches, several pharmaceutical companies have been successful in identifying potentially useful compounds for treating HCV infections. This article provides an overview of some of the small-molecule inhibitors that have shown promise so far in clinical trials and which could reach the clinic within the next three years.

Structure-based discovery of triphenylmethane derivatives as inhibitors of hepatitis C virus helicase

Hepatitis C virus nonstructural protein 3 (HCV NS3) helicase is believed to be essential for viral replication and has become an attractive target for the development of antiviral drugs. A fluorescence resonant energy transfer helicase assay was established for fast screening of putative inhibitors selected from virtual screening using the program DOCK. Soluble blue HT (1) was first identified as a novel HCV helicase inhibitor. Crystal structure of the NS3 helicase in complex with soluble blue HT shows that the inhibitor bears a significantly higher binding affinity mainly through a 4-sulfonatophenylaminophenyl group, and this is consistent with the activity assay. Subsequently, fragment-based searches were utilized to identify triphenylmethane derivatives for more potent inhibitors. Lead optimization resulted in a 3-bromo-4-hydroxyl substituted derivative 12 with an EC(50) value of 2.72 microM to Ava.5/Huh-7 cells and a lower cytotoxicity to parental Huh-7 cells (CC(50) = 10.5 microM), and it indeed suppressed HCV replication in the HCV replicon cells. Therefore, these inhibitors with structural novelty may serve as a useful scaffold for the discovery of new HCV NS3 helicase inhibitors.

Screening a peptide library by DSC and SAXD: comparison with the biological function of the parent proteins

We have recently identified the membranotropic regions of the hepatitis C virus proteins E1, E2, core and p7 proteins by observing the effect of protein-derived peptide libraries on model membrane integrity. We have studied in this work the ability of selected sequences of these proteins to modulate the L_β-L_α and L_α-H_II phospholipid phase transitions as well as check the viability of using both DSC and SAXD to screen a protein-derived peptide library. We demonstrate that it is feasible to screen a library of peptides corresponding to one or several proteins by both SAXD and DSC. This methodological combination should allow the identification of essential regions of membrane-interacting proteins which might be implicated in the molecular mechanism of membrane fusion and/or budding.

Natural products as promising drug candidates for the treatment of hepatitis B and C

Hepatitis B virus (HBV) or hepatitis C virus (HCV) infections are a major threat worldwide. Combination therapy of interferon-alpha and ribavirin is currently the treatment of choice for HCV-infected patients. However, this regimen is only effective in approximately 50% of patients and provokes severe side-effects. Numerous natural alternatives for treating HCV have been suggested. Deoxynojirimycin and its derivatives are iminosugars which exert anti-HCV activity by inhibiting alpha-glucosidases. A non-immunosuppressive derivate of cyclosporine A, NIM811, exerts anti-HCV activity by binding to cyclophilin. Other natural products with promising anti-HCV activity are 2-arylbenzofuran derivatives, Mellein, and pseudoguaianolides. For HBV treatment, several drugs are available, specifically targeting the virus polymerase (lamivudine, entecavir, telbivudine, and adefovir dipivoxil). The efficacy of these drugs is hampered by the development of resistance due to point mutations in the HBV polymerase. Due to drug resistance and adverse side-effects, the search for novel drugs is mandatory. Wogonin, ellagic acid, artemisinin and artesunate, chrysophanol 8-O-beta-D-glucoside, saikosaponin C, and protostane triterpenes are active against HBV. Natural products need to be investigated in more detail to explore their potential as novel adjuncts to established HBV or HCV therapy.

Immunotherapy for HCV infection: next steps

With more than 170 million individuals currently infected, HCV is a global pandemic, effecting approximately 3% of the entire world's population. HCV infection is a growing infectious disease pandemic with approximately 3-4 million new cases reported each year. Due to the persistent nature of the virus, 70-90% of infected individuals will develop chronic infection, which can lead to progressive liver disease including cirrhosis and hepatocellular carcinoma. Current standard treatment with a combination of IFN-alpha and ribavirin has improved the prognosis for many HCV sufferers; however, infection is very difficult to treat successfully and the protocol for treatment is neither simple, well tolerated nor economically favorable. Standard treatment can cost an average of US$22,000, and depending on genotype, as few as 42% of treated individuals will clear the infection. This collection of treatment issues combined with new concepts in immune therapy serve to underscore an urgent need for the development of improved immunotherapies, such as novel interferons, and support the possible development of therapeutic vaccines for the treatment of chronic HCV infection.

Hepatitis C virus core protein binding to lipid membranes: the role of domains 1 and 2

We have analysed and identified different membrane-active regions of the Hepatitis C virus (HCV) core protein by observing the effect of 18-mer core-derived peptide libraries from two HCV strains on the integrity of different membrane model systems. In addition, we have studied the secondary structure of specific membrane-interacting peptides from the HCV core protein, both in aqueous solution and in the presence of model membrane systems. Our results show that the HCV core protein region comprising the C-terminus of domain 1 and the N-terminus of domain 2 seems to be the most active in membrane interaction, although a role in protein-protein interaction cannot be excluded. Significantly, the secondary structure of nearly all the assayed peptides changes in the presence of model membranes. These sequences most probably play a relevant part in the biological action of HCV in lipid interaction. Furthermore, these membranotropic regions could be envisaged as new possible targets, as inhibition of its interaction with the membrane could potentially lead to new vaccine strategies.

Interaction of the most membranotropic region of the HCV E2 envelope glycoprotein with membranes. Biophysical characterization

The previously identified membrane-active regions of the hepatitis C virus (HCV) E1 and E2 envelope glycoproteins led us to identify different segments that might be implicated in viral membrane fusion, membrane interaction, and/or protein-protein binding. HCV E2 glycoprotein contains one of the most membranotropic segments, segment 603-634, which has been implicated in CD81 binding, E1/E2 and E2/E2 dimerization, and membrane interaction. Through a series of complementary experiments, we have carried out a study of the binding and interaction with the lipid bilayer of a peptide corresponding to segment 603-634, peptide E2(FP), as well as the structural changes induced by membrane binding that take place in both the peptide and the phospholipid molecules. Here, we demonstrate that peptide E2(FP) binds to and interacts with phospholipid model membranes, modulates the polymorphic phase behavior of membrane phospholipids, is localized in a shallow position in the membrane, and is probably oligomerized in the presence of membranes. These data support the role of E2(FP) in HCV-mediated membrane fusion, and sustain the notion that this segment of the E2 envelope glycoprotein, together with other segments of E2 and E1 glycoproteins, provides the driving force for the merging of the viral and target cell membranes.

A molecular chaperone glucose-regulated protein 94 blocks apoptosis induced by virus infection

The hepatitis C virus (HCV) E2 protein has been shown to block apoptosis and has been suggested to facilitate persistent infection of the virus. Here, we report that the anti-apoptotic activity of E2 is mediated by activation of nuclear factor kappa B (NF-kappaB) that directs expression of survival gene products such as tumor necrosis factor (TNF-alpha) receptor-associated factor 2 (TRAF2), X-chromosome-linked inhibitor of apoptosis protein (XIAP), FLICE-like inhibitory protein (FLIP), and survivin. Increased levels of these proteins were observed in HCV-infected cells and a cell line producing HCV E2 protein. The activation of NF-kappaB was mediated by HCV-E2-induced expression of the molecular chaperone glucose-regulated protein 94 (GRP94). Overexpression of GRP94 alone resulted in expression of anti-apoptotic proteins and blocked apoptosis induced by tumor-necrosis-related apoptosis-inducing ligand (TRAIL). Interestingly, increased levels of GRP94 were observed in cells supporting HCV proliferation that originated from liver tissues from HCV patients. Moreover, small interfering RNA (siRNA) knock-down of GRP94 nullified the anti-apoptotic activity of HCV E2.

CONCLUSION

These data indicate that HCV E2 blocks apoptosis induced by HCV infection and the host immune system through overproduction of GRP94, and that HCV E2 plays an important role in persistent HCV infection.

Identification of the membrane-active regions of hepatitis C virus p7 protein: biophysical characterization of the loop region

We have identified the membrane-active regions of the hepatitis C virus p7 protein by performing an exhaustive study of membrane rupture, hemifusion, and fusion induced by a p7-derived peptide library on model membranes having different phospholipid compositions. We report the identification in p7 of a highly membranotropic region located at the loop domain of the protein. Here, we have investigated the interaction of a peptide patterned after the p7 loop (peptide p7(L)), studying its binding and interaction with the lipid bilayer, and evaluated the binding-induced structural changes of the peptide and the phospholipids. We show that positively rich p7(L) strongly binds to negatively charged phospholipids and it is localized in a shallow position in the bilayer. Furthermore, peptide p7(L) exhibits a high tendency to oligomerize in the presence of phospholipids, which could be the driving force for the formation of the active ion channel. Therefore, our findings suggest that the p7 loop could be an attractive candidate for antiviral drug development, because it could be a target for antiviral compounds that may lead to new vaccine strategies.

Quasispecies and its impact on viral hepatitis

Quasispecies dynamics mediates adaptability of RNA viruses through a number of mechanisms reviewed in the present article, with emphasis on the medical implications for the hepatitis viruses. We discuss replicative and non-replicative molecular mechanisms of genome variation, modulating effects of mutant spectra, and several modes of viral evolution that can affect viral pathogenesis. Relevant evolutionary events include the generation of minority virus variants with altered functional properties, and alterations of mutant spectrum complexity that can affect disease progression or response to treatment. The widespread occurrence of resistance to antiviral drugs encourages new strategies to control hepatic viral disease such as combination therapies and lethal mutagenesis. In particular, ribavirin may be exerting in some cases its antiviral activity with participation of its mutagenic action. Despite many unanswered questions, here we document that quasispecies dynamics has provided an interpretation of the adaptability of the hepatitis viruses, with features conceptually similar to those observed with other RNA viruses, a reflection of the common underlying Darwinian principles.