Future treatments for hepatitis delta virus infection

Addressing hepatitis delta in primary care practices in the US: a narrative review

OBJECTIVE

Infection with the hepatitis delta virus (HDV), a unique RNA virus that requires hepatitis B virus (HBV) antigens for its assembly, replication, and transmission, causes severe viral hepatitis. Compared to HBV monoinfection, HDV infection increases the risk of severe liver disease, necessity for liver transplant, and mortality. Global HDV prevalence estimates vary from 5% to 15% among persons with HBV, but screening guidelines for HDV are inconsistent; some recommend risk-based screening, while others recommend universal screening for all people with HBV. Among primary care providers (PCPs) in the US, there is a lack of awareness and/or insufficient adherence to current recommendations for the screening of HDV infection and management of chronic HDV.

METHODS

Publications were obtained by conducting literature searches between July and August 2022 using the PubMed database and by manual searches of the retrieved literature for additional references. Information was synthesized to highlight HDV screening and management strategies for PCPs. Best practices for PCPs based on current guidelines and comanagement strategies for patients with HBV and HDV infection were summarized.

RESULTS

We recommend universal screening for HDV in patients positive for hepatitis B surface antigen. Confirmed HDV infection should prompt evaluation by a liver specialist, if available, with whom the PCP can comanage the patient. PCPs should counsel patients on the expected course of the disease, lifestyle factors that may influence liver health, need for consistent disease monitoring and follow-up, and risk of disease transmission. Screening is suggested for sexual partners, household contacts, and family members, with HBV immunization recommended for those found to be susceptible. There are currently no US Food and Drug Administration-approved therapies for HDV infection; thus, management is limited to treatments for chronic HBV infection plus long-term monitoring of liver health.

CONCLUSIONS

PCPs can be a valuable point of care for patients to access HDV/HBV screening, HBV immunization, and education, and can comanage patients with HBV and/or HDV infection.

Ergosterol peroxide blocks HDV infection as a novel entry inhibitor by targeting human NTCP receptor

Hepatitis D virus (HDV), which co-infects or superinfects patients with hepatitis B virus, is estimated to affect 74 million people worldwide. Chronic hepatitis D is the most severe form of viral hepatitis and can result in liver cirrhosis, liver failure, and hepatocellular carcinoma (HCC). Currently, there are no efficient HDV-specific drugs. Therefore, there is an urgent need for novel HDV therapies that can achieve a functional cure or even eliminate the viral infection. In the HDV life cycle, agents targeting the entry step of HDV infection preemptively reduce the intrahepatic viral RNA. Human sodium taurocholate co-transporting polypeptide (hNTCP), a transporter of bile acids on the plasma membrane of hepatocytes, is an essential entry receptor of HDV and is a promising molecular target against HDV infection. Here, we investigated the effect of ergosterol peroxide (EP) on HDV infection in vitro and in vivo. EP inhibited HDV infection of hNTCP-expressing dHuS-E/2 hepatocytes by interrupting the early fusion/endocytosis step of HDV entry. Furthermore, molecular modeling suggested that EP hinders LHBsAg binding to hNTCP by blocking access to S267 and V263. In addition, we generated hNTCP-expressing transgenic (Tg) C57BL/6 mice using the Cre/loxP system for in vivo study. EP reduced the liver HDV RNA level of HDV-challenged hNTCP-Cre Tg mice. Intriguingly, EP downregulated the mRNA level of liver IFN-γ. We demonstrate that EP is a bona fide HDV entry inhibitor that acts on hNTCP and has the potential for use in HDV therapies.

Test All for Hepatitis B Virus: Link to Care and Treatment if Quantitative DNA Positive, Vaccinate if Susceptible

Hepatitis B infection affects approximately 262 million people worldwide and is responsible for 900,000 deaths annually. This article reviews the major factors limiting HBV elimination, which includes limited linkage to care and complicated HBV testing and treatment guidelines. The article then provides solutions to these pressing issues.

Hepatitis Delta Infection: A Clinical Review

First discovered over 40 years ago, the hepatitis delta virus (HDV) is a unique RNA virus, requiring hepatitis B virus (HBV) antigens for its assembly, replication, and transmission. HBV and HDV can be acquired at the same time (coinfection) or HDV infection can occur in persons with chronic HBV (superinfection). Screening guidelines for HDV are inconsistent. While some guidelines recommend universal screening for all people with HBV, others recommend risk-based screening. Estimates of the global HDV prevalence range from 4.5 to 14.6% among persons with HBV; thus, there may be up to 72 million individuals with HDV worldwide. HDV is the most severe form of viral hepatitis. Compared to HBV monoinfection, HDV coinfection increases the risk of cirrhosis, hepatocellular carcinoma, hepatic decompensation, mortality, and necessity for liver transplant. Despite the severity of HDV, there are few treatment options. Pegylated interferon (off-label use) has long been the only available treatment, although bulevirtide is conditionally approved in some European countries. There are many potential treatments in development, but as yet, there are few effective and safe therapies for HDV infection. In conclusion, given the severity of HDV disease and the paucity of treatments, there is a great unmet need for HDV therapies.

Chronic hepatitis delta cirrhosis cured by adapting PEG-IFNα-2a + tenofovir disoproxil fumarate treatment duration until HBsAg loss

As the loss of HBsAg during treatment of chronic hepatitis delta (CHD) is mandatory for definitive clearance and durable response, the optimal target of therapy should be complete response (CR), defined as loss of HDV RNA and HBsAg, plus development of anti-HBs. The optimal treatment duration of CHD is not well established. We present 2 cases of patients with CHD cirrhosis who were treated with prolonged Peg-IFNα-2a + tenofovir disoproxil fumarate until HBsAg loss, and who achieved CR after 46 and 55 months of treatment respectively. A personalized approach and prolonged treatment duration determined by HBsAg loss may increase the likelihood of CR in CHD.

A Review of the Systemic Manifestations of Hepatitis B Virus Infection, Hepatitis D Virus, Hepatocellular Carcinoma, and Emerging Therapies

Chronic hepatitis B virus (HBV) infection affects about 262 million people worldwide, leading to over 820,000 deaths each year primarily due to cirrhosis and hepatocellular carcinoma. The World Health Organization has pledged to eliminate HBV as a health threat by 2030, but currently, no countries are on track to achieve this goal. One of the barriers to HBV elimination is stigma, causing shame, denial, self-isolation, self-rejection, and depression leading to those with chronic HBV less likely to get tested or seek treatment and more likely to conceal their infection. Other barriers include limited access to care and complicated and restrictive clinical practice guidelines. Increasing public and political efforts are necessary to raise awareness, increase access to care, and change screening and treatment guidelines. The current guidance of the American Association for the Study of Liver Diseases (AASLD) recommends testing only if patients are considered at risk, but this has proven to be ineffective. We propose a simplified "test all and treat all" approach with a 5-line guideline for HBV infection. Universal screening and treatment of adults is cost-effective and can prevent transmission by effectively managing chronic HBV. All patients who are hepatitis B surface antigen (HBsAg) positive with detectable HBV-DNA should receive treatment until HBsAg is undetectable for 12 months, as HBV-DNA transmission via blood transfusion can occur even at low viral loads of 16 copies/mL, and mother-to-child transmission is still a risk even with passive-active immunoprophylaxis. Furthermore, clinical outcomes after HBsAg clearance are significantly better than the clinical outcomes of those who remain HBsAg positive.

The Delta Delta: Gaps in screening and patient assessment for hepatitis D virus infection

Hepatitis D virus (HDV) infection is highly prevalent in patients with chronic hepatitis B (CHB). AASLD guidelines recommend a risk-based screening approach. Our aim was to ascertain if the risk-based approach leads to appropriate HDV screening, identify targets to improve screening rates, and study HDV clinical burden. CHB patients screened for HDV from 01/2016 to 12/2021 were identified. Level of training and specialty of providers ordering HDV screening tests were determined. HDV seropositive (HDV+) patient charts were reviewed for the presence of individual risk factors per the AASLD guidelines to determine if they met screening criteria. The severity of liver disease at the time of HDV screening was compared between the HDV+ group and a matched (based on age, hepatitis B e antigen status, BMI and sex) HDV seronegative (HDV-) group. During the study period, 1444/11,190 CHB patients were screened for HDV. Most screening tests were ordered by gastroenterology (90.2%) specialists and attending physicians (80.5%). HDV+ rate was 88/1444 (6%), and 72 HDV+ patients had complete information for analysis. 18% of HDV+ patients would be missed by a risk-based screening approach due to unreported or negative risk factors (see Table). A significantly higher number of HDV+ patients had developed significant fibrosis (p = 0.001) and cirrhosis (p < 0.01) by the time of screening than HDV- (n = 67) patients. In conclusion, targeted interventions are needed towards trainees and primary care clinics to improve screening rates. Current risk-based criteria do not appropriately screen for HDV. It is time for universal screening of HDV in CHB patients.

Epidemiology, presentation, and therapeutic approaches for hepatitis D infections

INTRODUCTION

Chronic Hepatitis D virus (HDV) infection remains an important global public health problem, with a changing epidemiological landscape over the past decade along with widespread implementation of hepatitis B vaccination and human migration. The landscape of HDV treatments has been changing, with therapies that have been under development for the last decade now in late stage clinical trials. The anticipated availability of these new therapies will hopefully replace the current therapies which are minimally effective.

AREAS COVERED

This narrative review discusses the clinical course, screening and diagnosis, transmission risk factors, epidemiology, current and investigational therapies, and liver transplantation in HDV. Literature review was performed using PubMed and ClinicalTrials.gov and includes relevant articles from 1977 to 2022.

EXPERT OPINION

HDV infection is an important global public health issue with a true prevalence that is still unknown. The distribution of HDV infection has changed globally with the availability of HBV vaccination and patterns of human migration. As HDV infection is associated with accelerated disease courses and poor outcomes, the global community needs to agree upon a uniform HDV screening strategy to understand the truth of global prevalence such that new therapies can target appropriate individuals as they become available in the future.

Medical Advances in Hepatitis D Therapy: Molecular Targets

An approximate number of 250 million people worldwide are chronically infected with hepatitis B virus, making them susceptible to a coinfection with hepatitis D virus. The superinfection causes the most severe form of a viral hepatitis and thus drastically worsens the course of the disease. Until recently, the only available therapy consisted of interferon-α, only eligible for a minority of patients. In July 2020, the EMA granted Hepcludex conditional marketing authorization throughout the European Union. This first-in-class entry inhibitor offers the promise to prevent the spread in order to gain control and eventually participate in curing hepatitis B and D. Hepcludex is an example of how understanding the viral lifecycle can give rise to new therapy options. Sodium taurocholate co-transporting polypeptide, the virus receptor and the target of Hepcludex, and other targets of hepatitis D therapy currently researched are reviewed in this work. Farnesyltransferase inhibitors such as Lonafarnib, targeting another essential molecule in the HDV life cycle, represent a promising target for hepatitis D therapy. Farnesyltransferase attaches a farnesyl (isoprenyl) group to proteins carrying a C-terminal Ca1a2X (C: cysteine, a: aliphatic amino acid, X: C-terminal amino acid) motif like the large hepatitis D virus antigen. This modification enables the interaction of the HBV/HDV particle and the virus envelope proteins. Lonafarnib, which prevents this envelopment, has been tested in clinical trials. Targeting the lifecycle of the hepatitis B virus needs to be considered in hepatitis D therapy in order to cure a patient from both coexisting infections. Nucleic acid polymers target the hepatitis B lifecycle in a manner that is not yet understood. Understanding the possible targets of the hepatitis D virus therapy is inevitable for the improvement and development of a sufficient therapy that HDV patients are desperately in need of.

Efficacy and Safety of Bulevirtide plus Tenofovir Disoproxil Fumarate in Real-World Patients with Chronic Hepatitis B and D Co-Infection

Background: The hepatitis B and D virus (HBV/HDV) hepatocyte entry inhibitor bulevirtide (BLV) has been available in Europe since July 2020, after the registrational trial MYR202. Real-life data on the efficacy and safety of BLV are sparse. Methods: We have analysed the course of treatment with BLV (2 mg/day) plus tenofovir disoproxil fumarate (TDF) (245 mg/day) in patients with chronic hepatitis delta (CHD). Virologic (≥2 log reduction in HDV RNA or suppression of HDV RNA below the lower limit of detection) and biochemical (normalisation of serum ALT) treatment responses after 24 weeks were defined according to the MYR202 trial. Results: Seven patients were recruited (four with liver cirrhosis Child−Pugh A). After 24 weeks, a virologic response was observed in five of seven and a biochemical response was seen in three of six patients with elevated serum ALT at baseline. Extended treatment data > 48 weeks were available in three cases: two presented with continuous virologic and biochemical responses and in one individual an HDV-RNA breakthrough was observed. Adverse effects were not recorded. Conclusions: The first real-life data of the approved dosage of 2 mg of BLV in combination with TDF confirm the safety, tolerability, and efficacy of the registrational trial MYR202 for a treatment period of 24 weeks and beyond.

Viral hepatitis: Past, present, and future

Each hepatitis virus-Hepatitis A, B, C, D, E, and G-poses a distinct scenario to the patient and clinician alike. Since the discovery of each virus, extensive knowledge regarding epidemiology, virologic properties, and the natural clinical and immunologic history of acute and chronic infections has been generated. Basic discoveries about host immunologic responses to acute and chronic viral infections, combined with virologic data, has led to vaccines to prevent Hepatitis A, B, and E and highly efficacious antivirals for Hepatitis B and C. These therapeutic breakthroughs are transforming the fields of hepatology, transplant medicine in general, and public and global health. Most notably, there is even an ambitious global effort to eliminate chronic viral hepatitis within the next decade. While attainable, there are many barriers to this goal that are being actively investigated in basic and clinical labs on the local, national, and international scales. Herein, we discuss pertinent clinical information and recent organizational guidelines for each of the individual hepatitis viruses while also synthesizing this information with the latest research to focus on exciting future directions for each virus.

Present and future management of viral hepatitis

Viral hepatitis can result in important morbidity and mortality, with its impact on health conditioned by the specific type of hepatitis, the geographical region of presentation and the development and access to new drugs, among other factors. Most acute presentation forms are self-limiting and may even go unnoticed, with just a small percentage of cases leading to acute liver failure that may necessitate transplantation or even cause the death of the patient. However, when they become chronic, as in the case of hepatitis B virus and C virus, unless they are diagnosed and treated adequately they may have severe consequences, like cirrhosis or hepatocarcinoma. Understanding of the mechanisms of transmission, the pathogenesis, the presence of vaccinations and the development over recent years of new highly-efficient, potent drugs have meant that we are now faced with a new scenario in the management of viral hepatitis, particularly hepatitis B virus and hepatitis C virus. The spectacular advances in hepatitis C virus treatment have led the World Health Organization to propose the objective of its eradication by 2030. The key aspect to achieving this goal is to ensure that these treatments reach all the more vulnerable population groups, in whom the different types of viral hepatitis have a high prevalence and constitute a niche that may perpetuate infection and hinder its eradication. Accordingly, micro-elimination programs assume special relevance at the present time.

Efficacy and safety of bulevirtide in patients with chronic hepatitis D and compensated cirrhosis

Aim. To study the efficacy and safety of bulevirtide, the HBV and HDV entry inhibitor. Materials and methods. Analysis of the results of using bulevirtide in randomized controlled open-label comparative studies MYR202 and MYR203 in 56 patients with chronic hepatitis D and compensated cirrhosis, in monotherapy and combination with pegylated interferon alpha-2a (PEG-IFN). Results. Monotherapy with bulevirtide for 24 weeks in the MYR202 study in 46 patients with compensated liver cirrhosis demonstrated: 1) a high rate of virological (100%) and biochemical response (alanine aminotransferase normalization rate 45.7%), 2) superiority of bulevirtide in efficacy over the control group (tenofovir), 3) comparability of treatment efficacy in patients with and without cirrhosis, 4) no progression of liver fibrosis with elastometry in most patients. Treatment with bulevirtide in monotherapy and combination with PEG-IFN for 48 weeks in 10 patients with compensated liver cirrhosis in the MYR203 study was accompanied by a high rate of virological response (80%) and normalization of alanine aminotransferase (70%). Bulevirtide was well tolerated, there was no deterioration in tolerability compared with patients without cirrhosis, there were no serious adverse events and cases of treatment cancellation due to adverse events. Conclusion. Bulevirtide is recommended as the first line of treatment for chronic hepatitis D in patients with compensated cirrhosis in monotherapy and combination with PEG-IFN.

Hepatitis delta in patients hospitalized in Spain (1997-2018)

BACKGROUND

Hepatitis delta is the most aggressive form of chronic viral hepatitis. We examined the clinical burden, epidemiological features and time trends for hepatitis delta patients hospitalized in Spain during the last two decades.

METHODS

Retrospective, observational study using the Spanish National Registry of Hospital Discharges. Information was retrieved since 1997 to 2018.

RESULTS

From a total of 79 647 783 nationwide hospital admissions recorded during the study period, 5179 included hepatitis delta as diagnosis. The overall hospitalization rate because of hepatitis delta was 6.5/105, without significant yearly changes. In-hospital death occurred in 335 (6.6%) patients. Acute hepatitis and cirrhosis were recorded in 46.5 and 33.5% of hepatitis delta hospitalizations, respectively. Acute hepatitis delta predominated until 2007 (55.9%) whereas cirrhosis increased since then (39.4%). Hepatic decompensation events and liver cancer accounted on average for 16 and 8% of hospitalizations, increasing significantly over time. Coinfection with HIV and hepatitis C virus (HCV) were recognized in 24 and 31.2% of hepatitis delta patients, respectively. All hepatitis C, HIV and injection drug use declined significantly since 2008.

CONCLUSION

The rate of hepatitis delta in patients hospitalized in Spain is low and has remained stable over two decades. However, hepatitis delta-related decompensation events and liver cancer are on the rise. The association of hepatitis delta with injection drug use, HIV and HCV has declined among recently hospitalized hepatitis delta patients.

Cell Culture Models for the Study of Hepatitis D Virus Entry and Infection

Chronic hepatitis D is one of the most severe and aggressive forms of chronic viral hepatitis with a high risk of developing hepatocellular carcinoma (HCC). It results from the co-infection of the liver with the hepatitis B virus (HBV) and its satellite, the hepatitis D virus (HDV). Although current therapies can control HBV infection, no treatment that efficiently eliminates HDV is available and novel therapeutic strategies are needed. Although the HDV cycle is well described, the lack of simple experimental models has restricted the study of host–virus interactions, even if they represent relevant therapeutic targets. In the last few years, the discovery of the sodium taurocholate co-transporting polypeptide (NTCP) as a key cellular entry factor for HBV and HDV has allowed the development of new cell culture models susceptible to HBV and HDV infection. In this review, we summarize the main in vitro model systems used for the study of HDV entry and infection, discuss their benefits and limitations and highlight perspectives for future developments.

Viral hepatitis update: Progress and perspectives

Viral hepatitis, secondary to infection with hepatitis A, B, C, D, and E viruses, are a major public health problem and an important cause of morbidity and mortality. Despite the huge medical advances achieved in recent years, there are still points of conflict concerning the pathogenesis, immune response, development of new and more effective vaccines, therapies, and treatment. This review focuses on the most important research topics that deal with issues that are currently being solved, those that remain to be solved, and future research directions. For hepatitis A virus we will address epidemiology, molecular surveillance, new susceptible populations as well as environmental and food detections. In the case of hepatitis B virus, we will discuss host factors related to disease, diagnosis, therapy, and vaccine improvement. On hepatitis C virus, we will focus on pathogenesis, immune response, direct action antivirals treatment in the context of solid organ transplantation, issues related to hepatocellular carcinoma development, direct action antivirals resistance due to selection of resistance-associated variants, and vaccination. Regarding hepatitis D virus, we describe diagnostic methodology, pathogenesis, and therapy. Finally, for hepatitis E virus, we will address epidemiology (including new emerging species), diagnosis, clinical aspects, treatment, the development of a vaccine, and environmental surveillance.

Prevalence of hepatitis delta virus among chronic hepatitis B carriers in a large tertiary center in the Netherlands

BACKGROUND & AIMS

Hepatitis D virus infection (HDV) is considered the most severe form of viral hepatitis. In this study, we aimed to evaluate the prevalence of HDV infection in a tertiary center of a large, multi-ethnic city in the Netherlands. Moreover, we validate the reliability of a novel anti-HDV CLIA assay.

METHODS

All HBsAg-positive patients visiting the outpatient clinic between 2017 and 2019 were tested for HDV serology. Seropositive serum samples were further assessed by HDV RNA PCR and Sanger sequencing to identify the HDV genotype.

RESULTS

The CLIA assay was 100% sensitive and 98% specific. Out of 925 patients 3.7% tested seropositive for HDV, and HDV viremia was confirmed in 2.0%. The majority of patients had a non-Dutch background and did not speak English or Dutch. We detected HDV genotype 5 (N = 3), and genotype 1 (N = 15). Phylogenetic analysis demonstrated HDV1 clusters composed of sub-Saharan Africa isolates, central Asian, Turkish, Iranian and European isolates.

CONCLUSIONS

The prevalence of HDV infection in a tertiary center in the Netherlands was 2.0% among HBsAg-positive individuals, and mainly in non-Dutch individuals. Only HDV genotype 1 and 5 isolates were detected, which was found to match with the patient's country of origin.

Investigating the prevalence and clinical effects of hepatitis delta viral infection in Taiwan

PURPOSE

To clarify and investigate the prevalence and clinical impact of hepatitis D virus (HDV) infection in Taiwan's communities.

METHODS

HDV infection in patients with chronic hepatitis B viral (HBV) infection was examined using an anti-HDV antibody in Yonghe Cardinal Tien Hospital (YCTH), a district hospital in Taiwan. Clinical characteristics of anti-HDV-positive and anti-HDV-negative patients were collected and compared. These characteristics were also compared with the data collected from a medical center. Continuous variables and confounding factor adjustments were compared using the analysis of covariance method, whereas categorical variables were compared using the logistic regression method.

RESULTS

A total of 346 patients with chronic HBV infection were assessed from 2018 to 2019. Among them, 4 (1.15%) were positive for anti-HDV. The clinical, virological, and biochemical characteristics were similar between anti-HDV-positive and anti-HDV-negative groups. None of the four patients was positive for serum HDV RNA. Another 18 anti-HDV-positive patients were identified from National Taiwan University Hospital (NTUH). The clinical, virological, and biochemical characteristics of anti-HDV-positive patients from YCTH and NTUH were also similar.

CONCLUSION

The prevalence of HDV and the serum HDV RNA-positive rate were low in district hospitals in Taiwan. Coexisting HDV infection did not influence the clinical manifestation of patients with chronic HBV infection in Taiwan. However, because the number of HDV RNA cases was very small, our findings may not be conclusive. Besides, since the sensitivity of current anti-HDV kit is not 100%, more sensitive methods are needed to achieve reliable prevalence data.

New therapies for hepatitis delta virus infection

Hepatitis delta virus (HDV) infection is a defective virus requiring hepatitis B virus (HBV) for its complete replication cycle. HDV is a small hepatotropic RNA virus and around 15 to 25 million people worldwide are living with chronic hepatitis delta (CHD) infection. However, the prevalence of HDV may be underestimated, and screening is frequently insufficient. HDV infection remains endemic in several regions including Central and West Africa, the Mediterranean basin, the Middle East, Eastern Europe, Northern Asia, certain areas of Southeast Asia and the Amazon basin of South America. The best preventive strategy to decrease HDV infection is to improve coverage of the prophylactic HBV vaccine. HDV infection may occur by HBV-HDV co-infection or superinfection, and the latter is usually more severe. CHD is associated with a higher risk of cirrhosis and hepatocellular carcinoma (HCC) compared to HBV mono-infection. Pegylated interferon alpha (PEG-IFNα) therapy is limited by moderate effectiveness (around 20%) and its adverse effects. The entry inhibitor, bulevirtide (BLV, Hepcludex^® ), which was recently approved in Europe at a dose of 2 mg in sub-cutaneous injection per day, is indicated for the treatment of CHD in adult patients with compensated liver disease and positive HDV viremia. BLV can be administrated in monotherapy or in combination with PEG-IFNα. Nucleos(t)ide analogues can be used in combination for underlying HBV infection. The optimal treatment duration has not yet been determined and treatment should be continued if a clinical benefit is observed. There are other promising therapies such as IFN lambda (IFNλ) (immunomodulator), lonafarnib (prenylation inhibitor) and nucleic acid polymers (Inhibitors of HBsAg release). In this review, we will present an update on CHD and future promising treatments.

Viral hepatitis: A brief introduction, review of management, advances and challenges

Viral hepatitis represents a major public health hazard and is associated with significant global mortality. Over the last decade, there have been significant developments in the prevention and treatment of viral hepatitis. These changes have led to a situation whereby global elimination has become a realistic goal, fully endorsed by the World Health Organization (WHO). By 2030, the WHO aims to reduce viral hepatitis mortality by 65% and reduce new infections by 90% by 2030. These are ambitious targets and will only be met through a sustained programme. This will require expertise from hepatologists and virologists and the fields of public health and primary care. In this article, we review the causes of viral hepatitis, its management through prevention and treatments, and the most pressing challenges and recent advances.

Long-term trans-inhibition of the hepatitis B and D virus receptor NTCP by taurolithocholic acid

Human hepatic bile acid transporter Na⁺/taurocholate cotransporting polypeptide (NTCP) represents the liver-specific entry receptor for the hepatitis B and D viruses (HBV/HDV). Chronic hepatitis B and D affect several million people worldwide, but treatment options are limited. Recently, HBV/HDV entry inhibitors targeting NTCP have emerged as promising novel drug candidates. Nevertheless, the exact molecular mechanism that NTCP uses to mediate virus binding and entry into hepatocytes is still not completely understood. It is already known that human NTCP mRNA expression is downregulated under cholestasis. Furthermore, incubation of rat hepatocytes with the secondary bile acid taurolithocholic acid (TLC) triggers internalization of the rat Ntcp protein from the plasma membrane. In the present study, the long-term inhibitory effect of TLC on transport function, HBV/HDV receptor function, and membrane expression of human NTCP were analyzed in HepG2 and human embryonic kidney (HEK293) cells stably overexpressing NTCP. Even after short-pulse preincubation, TLC had a significant long-lasting inhibitory effect on the transport function of NTCP, but the NTCP protein was still present at the plasma membrane. Furthermore, binding of the HBV/HDV myr-preS1 peptide and susceptibility for in vitro HDV infection were significantly reduced by TLC preincubation. We hypothesize that TLC rapidly accumulates in hepatocytes and mediates long-lasting trans-inhibition of the transport and receptor function of NTCP via a particular TLC-binding site at an intracellularly accessible domain of NTCP. Physiologically, this trans-inhibition might protect hepatocytes from toxic overload of bile acids. Pharmacologically, it provides an interesting novel NTCP target site for potential long-acting HBV/HDV entry inhibitors.NEW & NOTEWORTHY The hepatic bile acid transporter NTCP is a high-affinity receptor for hepatitis B and D viruses. This study shows that TLC rapidly accumulates in NTCP-expressing hepatoma cells and mediates long-lasting trans-inhibition of NTCP's transporter and receptor function via an intracellularly accessible domain, without substantially affecting its membrane expression. This domain is a promising novel NTCP target site for pharmacological long-acting HBV/HDV entry inhibitors.

SARS-CoV-2 and SARS-CoV: Virtual screening of potential inhibitors targeting RNA-dependent RNA polymerase activity (NSP12)

Since the outbreak of severe acute respiratory syndrome (SARS) in 2003, the harm caused by coronaviruses to the world cannot be underestimated. Recently, a novel coronavirus (severe acute respiratory syndrome coronavirus-2 [SARS-CoV-2]) initially found to trigger human severe respiratory illness in Wuhan City of China in 2019, has infected more than six million people worldwide by 21 June 2020, and which has been recognized as a public health emergency of international concern as well. And the virus has spread to more than 200 countries around the world. However, the effective drug has not yet been officially licensed or approved to treat SARS-Cov-2 and SARS-Cov infection. NSP12-NSP7-NSP8 complex of SARS-CoV-2 or SARS-CoV, essential for viral replication and transcription, is generally regarded as a potential target to fight against the virus. According to the NSP12-NSP7-NSP8 complex (PDB ID: 7BW4) structure of SARS-CoV-2 and the NSP12-NSP7-NSP8 complex (PDB ID: 6NUR) structure of SARS-CoV, NSP12-NSP7 interface model, and NSP12-NSP8 interface model were established for virtual screening in the present study. Eight compounds (Nilotinib, Saquinavir, Tipranavir, Lonafarnib, Tegobuvir, Olysio, Filibuvir, and Cepharanthine) were selected for binding free energy calculations based on virtual screening and docking scores. All eight compounds can combine well with NSP12-NSP7-NSP8 in the crystal structure, providing drug candidates for the treatment and prevention of coronavirus disease 2019 and SARS.

Hepatitis B Virus Cure: Targets and Future Therapies

Chronic hepatitis B virus (HBV) infection is a major global health problem. It can cause progressive liver fibrosis leading to cirrhosis with end-stage liver disease, and a markedly increased risk of hepatocellular carcinoma. In the last two decades, substantial progress has been made in the treatment of chronic hepatitis, B. However, HBV is often reactivated after stopping nucloes(t)ide analogues because antivirals alone do not directly target covalently closed circular DNA, which is the template for all viral RNAs. Therefore, although currently available antiviral therapies achieve suppression of HBV replication in the majority of patients, hepatitis B surface antigen (HBsAg) loss and seroconversion is rarely achieved despite long-term antiviral treatment (HBsAg loss of less than 10% in 5 years). Various clinical trials of agents that interrupt the HBV life cycle in hepatocytes have been conducted. Potential treatment strategies and new agents are emerging as HBV cure. A combination of current and new anti-HBV agents may increase the rate of HBsAg seroclearance; thus, optimized regimens must be validated. Here, we review the newly investigated therapeutic compounds and the results of preclinical and/or clinical trials.

Interplay between Hepatitis D Virus and the Interferon Response

Chronic hepatitis D (CHD) is the most severe form of viral hepatitis, with rapid progression of liver-related diseases and high rates of development of hepatocellular carcinoma. The causative agent, hepatitis D virus (HDV), contains a small (approximately 1.7 kb) highly self-pairing single-strand circular RNA genome that assembles with the HDV antigen to form a ribonucleoprotein (RNP) complex. HDV depends on hepatitis B virus (HBV) envelope proteins for envelopment and de novo hepatocyte entry; however, its intracellular RNA replication is autonomous. In addition, HDV can amplify HBV independently through cell division. Cellular innate immune responses, mainly interferon (IFN) response, are crucial for controlling invading viruses, while viruses counteract these responses to favor their propagation. In contrast to HBV, HDV activates profound IFN response through the melanoma differentiation antigen 5 (MDA5) pathway. This cellular response efficiently suppresses cell-division-mediated HDV spread and, to some extent, early stages of HDV de novo infection, but only marginally impairs RNA replication in resting hepatocytes. In this review, we summarize the current knowledge on HDV structure, replication, and persistence and subsequently focus on the interplay between HDV and IFN response, including IFN activation, sensing, antiviral effects, and viral countermeasures. Finally, we discuss crosstalk with HBV.

The emerging role and significance of circular RNAs in viral infections and antiviral immune responses: possible implication as theranostic agents

Circular RNAs (circRNAs) are ubiquitously expressed, covalently closed rings, produced by pre-mRNA splicing in a reversed order during post-transcriptional processing. Circularity endows 3'-5'-linked circRNAs with stability and resistance to exonucleolytic degradation which raises the question whether circRNAs may be relevant as potential therapeutic targets or agents. High stability in biological systems is the most remarkable property and a major criterion for why circRNAs could be exploited for a range of RNA-centred medical applications. Even though various biological roles and regulatory functions of circRNAs have been reported, their in-depth study is challenging because of their circular structure and sequence-overlap with linear mRNA counterparts. Moreover, little is known about their role in viral infections and in antiviral immune responses. We believe that an in-depth and detailed understanding of circRNA mediated viral protein regulations will increase our knowledge of the biology of these novel molecules. In this review, we aimed to provide a comprehensive basis and overview on the biogenesis, significance and regulatory roles of circRNAs in the context of antiviral immune responses and viral infections including hepatitis C virus infection, hepatitis B virus infection, hepatitis delta virus infection, influenza A virus infection, Epstein-Barr virus infection, kaposi's sarcoma herpesvirus infection, human cytomegalovirus infection, herpes simplex virus infection, human immunodeficiency virus infection, porcine epidemic diarrhoea virus infection, ORF virus infection, avian leukosis virus infection, simian vacuolating virus 40 infection, transmissible gastroenteritis coronavirus infection, and bovine viral diarrhoea virus infection. We have also discussed the critical regulatory role of circRNAs in provoking antiviral immunity, providing evidence for implications as therapeutic agents and as diagnostic markers.