New insights into hepatitis B virus biology and implications for novel antiviral strategies

Advancing beyond reverse transcriptase inhibitors: The new era of hepatitis B polymerase inhibitors

Hepatitis B virus (HBV) is a genetically diverse blood-borne virus responsible for chronic hepatitis B. The HBV polymerase plays a key role in viral genome replication within the human body and has been identified as a potential drug target for chronic hepatitis B therapeutics. However, available nucleotide reverse transcriptase inhibitors only target the reverse transcriptase domain of the HBV polymerase; they also pose resistance issues and require lifelong treatment that can burden patients financially. In this study, various chemical classes are reviewed that have been developed to target different domains of the HBV polymerase: Terminal protein, which plays a vital role in the formation of the viral DNA; Reverse transcriptase, which is responsible for the synthesis of the viral DNA from RNA, and; Ribonuclease H, which is responsible for degrading the RNA strand in the RNA-DNA duplex formed during the reverse transcription process. Host factors that interact with the HBV polymerase to achieve HBV replication are also reviewed; these host factors can be targeted by inhibitors to indirectly inhibit polymerase functionality. A detailed analysis of the scope and limitations of these inhibitors from a medicinal chemistry perspective is provided. The structure-activity relationship of these inhibitors and the factors that may affect their potency and selectivity are also examined. This analysis will be useful in supporting the further development of these inhibitors and in designing new inhibitors that can inhibit HBV replication more efficiently.

A Study on Pregenomic RNA and Factors Related to Hepatitis B Virus Infection Based on Real World

Objective

This article aims to study the influencing factors of pgRNA and its change magnitude based on the real world.

Methods

A total of 421 patients who were tested for pgRNA were selected. According to the baseline data, the subjects were divided into negative and positive groups. The Chi-square test and logistic regression were used to analyze the influencing factors of pgRNA status. Based on the follow-up data, the rank-sum test and linear regression were used to analyze the influencing factors of pgRNA change magnitude.

Results

A total of 153 (36.3%) of the 421 subjects were pgRNA-negative and 268 (63.7%) were pgRNA-positive. Logistic regression analysis showed that positive HBV DNA (OR: 40.51), positive HBeAg (OR: 66.24), tenofovir treatment (OR: 23.47), and entecavir treatment (OR: 14.90) were the independent risk factors for positive pgRNA. Univariate linear regression showed that the pgRNA change magnitude of patients treated with entecavir was higher than that of patients treated with tenofovir. Multivariate linear regression showed that age was an independent factor influencing pgRNA change magnitude.

Conclusions

The pgRNA of patients who were young, female, HBV DNA-positive, high-HBsAg, HBeAg-positive is higher than the detection line. HBV DNA and HBeAg are the independent risk factors of positive pgRNA. Different antiviral regimens and disease stages have significantly different effects on pgRNA status. There was a significant correlation between pgRNA and FIB-4, suggesting that pgRNA is related to liver fibrosis. The decrease in pgRNA was greater in young patients than in non-young patients. The decrease in pgRNA was greater in patients treated with tenofovir than in patients treated with entecavir.

Functional roles of GRP78 in hepatitis B virus infectivity and antigen secretion

Viruses utilize cellular proteins to mediate their life cycle. However, the hepatitis B virus (HBV) life cycle is still mysterious and remains to be elucidated. Here, GRP78/BiP/HSPA5, a 78 kDa glucose-regulated protein, was identified as a preS2 interacting protein. Pulldown assay showed the interaction of glucose-regulated protein 78 (GRP78) with both the preS2 domain-containing large S and middle S proteins expressed in a human hepatocellular cell line. The immunofluorescence studies revealed that the preS2 colocalized with GRP78. Interestingly, it was found that preS2 specifically bound to the ATPase domain of GRP78. To understand how GRP78 plays a role in HBV infection, stably GRP78-expressing cells were established, which promoted HBV infectivity and replication. In contrast, knockdown of GRP78 changed the HBV antigen secretion but not the viral DNA amplification. Taken together, these results suggest that GRP78 should interact with preS2 via the ATPase domain and modulate both the HBV infectivity and HBV antigen secretion.

A novel recombinant cccDNA-based mouse model with long term maintenance of rcccDNA and antigenemia

The covalently closed circular DNA (cccDNA) of hepatitis B virus (HBV) is critical for viral persistence in vivo. The lack of reliable, characterized and convenient small animal models for studying cccDNA persistence has long been a bottleneck for basic and translational research on HBV cure. A mouse model that can maintain intrahepatic cccDNA is urgently needed. Through combining the Cre/loxP-mediated recombination and adeno-associated virus (AAV) vector delivery strategy, we establish a novel recombinant cccDNA (rcccDNA) mouse model. AAV-rcccDNA mice supported long-term maintenance of intrahepatic rcccDNA which could be easily detected by Southern blotting within 30 weeks after transduction. Quantitative PCR could detect the rcccDNA signal throughout the experiment duration (>51 weeks). Furthermore, rcccDNA supported persistent serum antigenemia (>72 weeks) and intrahepatic HBsAg and HBcAg expression (>51 weeks). Flow cytometry analysis and single-cell RNA sequencing showed that AAV-rcccDNA mice displayed a compromised CD8⁺ T cell response. Meanwhile, minimal intrahepatic inflammation and fibrosis were observed. Furthermore, three anti-HBV compounds, AKEX0007, a post-transcriptional inhibitor, Bay 41-4109, a capsid allosteric modulator, and Entecavir were assessed in this AAV-rcccDNA mouse model. The changes of viral markers by these drugs were consistent with their mode of action although neither of them diminished the level of rcccDNA. This mouse model recapitulated the immune tolerant state of HBV infection with long term maintenance of cccDNA and antigenemia, which will provide a suitable platform for studying cccDNA persistence and developing intervention strategies that would eventually break the tolerance and clear the virus.

In Vitro Systems for Studying Different Genotypes/Sub-Genotypes of Hepatitis B Virus: Strengths and Limitations

Hepatitis B virus (HBV) infects the liver resulting in end stage liver disease, cirrhosis, and hepatocellular carcinoma. Despite an effective vaccine, HBV poses a serious health problem globally, accounting for 257 million chronic carriers. Unique features of HBV, including its narrow virus-host range and its hepatocyte tropism, have led to major challenges in the development of suitable in vivo and in vitro model systems to recapitulate the HBV replication cycle and to test various antiviral strategies. Moreover, HBV is classified into at least nine genotypes and 35 sub-genotypes with distinct geographical distributions and prevalence, which have different natural histories of infection, clinical manifestation, and response to current antiviral agents. Here, we review various in vitro systems used to study the molecular biology of the different (sub)genotypes of HBV and their response to antiviral agents, and we discuss their strengths and limitations. Despite the advances made, no system is ideal for pan-genotypic HBV research or drug development and therefore further improvement is required. It is necessary to establish a centralized repository of HBV-related generated materials, which are readily accessible to HBV researchers, with international collaboration toward advancement and development of in vitro model systems for testing new HBV antivirals to ensure their pan-genotypic and/or customized activity.

Role of alcohol in pathogenesis of hepatitis B virus infection

Hepatitis B virus (HBV) and alcohol abuse often contribute to the development of end-stage liver disease. Alcohol abuse not only causes rapid progression of liver disease in HBV infected patients but also allows HBV to persist chronically. Importantly, the mechanism by which alcohol promotes the progression of HBV-associated liver disease are not completely understood. Potential mechanisms include a suppressed immune response, oxidative stress, endoplasmic reticulum and Golgi apparatus stresses, and increased HBV replication. Certainly, more research is necessary to gain a better understanding of these mechanisms such that treatment(s) to prevent rapid liver disease progression in alcohol-abusing HBV patients could be developed. In this review, we discuss the aforementioned factors for the higher risk of liver diseases in alcohol-induced HBV pathogenies and suggest the areas for future studies in this field.

Exonuclease I and III improve the detection efficacy of hepatitis B virus covalently closed circular DNA

BACKGROUND

Hepatitis B virus covalently closed circular DNA (HBV cccDNA) is an important biomarker of hepatitis B virus infection. However, the current methods are not specific and sensitive. The present study aimed to develop a specific and sensitive assay method for the quantification of HBV cccDNA.

METHODS

Exonuclease I (Exo I) & Exonuclease III (Exo III) and specific primer probes are used in real-time PCR. The virus particles isolated from peripheral blood mononuclear cells were used as negative control and HBV1.3 recombinant plasmid 3.2 kb circular DNA fragment was used as positive control. The methods of cccDNA detection were evaluated in cell lines, plasmid, animal model, patient serum and liver biopsies.

RESULTS

A linear range of 10¹-10⁷ copies/assay using specific primers for HBV cccDNA was established. HBV cccDNA were only detected in cell lines, animal model and liver tissue. It cannot be detected in serum samples. Intrahepatic HBV cccDNA level had good correlation with intrahepatic total HBV DNA level (r = 0.765, P < 0.001).

CONCLUSIONS

The real-time quantitative PCR is an effective and feasible method for sensitive and specific detection of low copy number of cccDNA. The novel detection method is fast, provides high sensitivity and specificity and can be used in clinical practice.

Association between IL-37 gene polymorphisms and risk of HBV-related liver disease in a Saudi Arabian population

Interleukin-37 (IL-37) has recently been recognized as a strong anti-inflammatory cytokine having anti-tumor activity against hepatocellular carcinoma (HCC) in hepatitis B virus (HBV)-infected patients. HCC is a typical inflammation-related cancer, and genetic variations within the IL-37 gene may be associated with the risk of HBV infection. Identification of the allelic patterns that genetically have a high disease risk is essential for the development of preventive diagnostics for HBV-mediated liver disease pathogenesis. In this study, we aimed to investigate the association between single nucleotide polymorphisms (SNPs) within the IL-37 gene and disease sequelae associated with HBV infection. We genotyped ten IL-37 SNPs in 1274 patients infected with HBV and 599 healthy controls from a Saudi Arabian population. Among the selected SNPs, two SNPs (rs2723175 and rs2708973) were strongly associated with HBV infection, and six SNPs (rs2723176, rs2723175, rs2723186, rs364030, rs28947200, rs4392270) were associated with HBV clearance, comparing healthy controls and HBV infected-patients respectively. A suggestive association of rs4849133 was identified with active HBV surface antigen (HBsAg) carrier and HBV-related liver disease progression. In conclusion, our findings suggest that variations at the IL-37 gene may be useful as genetic predictive risk factors for HBV infection and HBV-mediated liver disease progression in the Saudi Arabian population.

The dynamics of integration, viral suppression and cell-cell transmission in the development of occult Hepatitis B virus infection

BACKGROUND

Out of several phases of HBV infection, the least understood phase is occult hepatitis B virus infection. The paucity of data due to non-availability of biological tissues and the prerequisite of ultra-sensitive assays for the detection of occult hepatitis B virus infection prompted us to utilize mathematical modeling in determining mechanisms that lead to occult hepatitis B virus infection and characteristics of HBV infection during occult hepatitis B virus infection.

METHODS

We proposed two mathematical models (M1 and M2), considering two different phenomenon for episomal maintenance and accumulation of covalently closed circular DNA (cccDNA) in infected hepatocytes: (i) M1 - recirculation of the relaxed circular DNA/double-stranded linear DNA from cytoplasm to the nucleus, and (ii) M2 - reinfection of infected hepatocytes with virions. We further incorporated the dynamics of integrated Hepatitis B virus DNA (iHBV) to investigate its role in the development of occult hepatitis B virus infection.

RESULTS

The analysis showed that the main mechanism for the spread of infection during occult hepatitis B virus infection is cell-to-cell transmission and not cell-free virus transmission. A significant viral suppression (of at least 99% from its peak production values) was essential but not sufficient in the development of occult hepatitis B virus infection under M1; however under M2, the viral suppression was neither sufficient nor essential as the inhibition of the production of HBsAg without viral suppression can also explain the development of occult hepatitis B virus infection. Our analysis also revealed that occult hepatitis B virus infection seropositive cases are more likely to progress into liver cirrhosis compared to occult hepatitis B virus infection seronegative cases. The iHBV was found to be mostly silent (by either being absent or non-productive for HBsAg) during occult hepatitis B virus infection.

CONCLUSION

The viral suppression is neither essential nor sufficient to explain the development of occult hepatitis B virus infection on its own. Not only the viral suppression but the inhibition -of the production and the export of HBsAg from cccDNA and iHBV also plays an important role in the development of occult hepatitis B virus infection. This is the first study, which incorporates the dynamics of iHBV and shows that HBV primarily spreads via cell-cell transmission during occult hepatitis B virus infection.

miR-200c targets nuclear factor IA to suppress HBV replication and gene expression via repressing HBV Enhancer I activity

BACKGROUND

Hepatitis B virus (HBV) chronic infection is a health problem in the worldwide, with a underlying higher risk of liver cirrhosis and hepaticocellular carcinoma. A number of studies indicate that microRNAs (miRNAs) play vital roles in HBV replication. This study was designed to explore the potential molecular mechanism of miR-200c in HBV replication.

METHODS

The expression of miR-200c, nuclear factor IA (NFIA) mRNA, HBV DNA, and HBV RNA (pregenomic RNA (pgRNA), and total RNA) were measured by qRCR. The levels of HBsAg and HBeAg were detected by ELISA. NFIA expression at protein level was measured by western blot. The direct interaction between miR-200c and NFIA were identified by Targetscan software and Dual-Luciferase reporter analysis. Enhance I activity were detected by Dual-Luciferase reporter assay.

RESULTS

miR-200c expression was prominently reduced in pHBV1.3-tranfected Huh7 and in stable HBV-producing cell line (HepG2.2.15). The enforced expression of miR-200c significantly suppressed HBV replication, as demonstrated by the reduced levels of HBV protein (HBsAg and HBeAg) and, DNA and RNA (pgRNA and total RNA) levels. NFIA was proved to be a target of miR-200c and NFIA overexpression notably stimulated HBV replication. In addition, the inhibitory effect of miR-200c on HBV Enhance I activity was abolished following restoration of NFIA.

CONCLUSIONS

miR-200c repressed HBV replication by directly targeting NFIA, which might provide a novel therapeutic target for HBV infection.

miR-146 promotes HBV replication and expression by targeting ZEB2

Hepatitis B virus (HBV) is associated with the development of a wide spectrum of liver diseases. The involvement of miRNAs in HBV replication is being gradually identified. Among these miRNAs, miR-146a expression was found to be positively correlated with HBV replication levels. However, the regulatory relationship between miR-146a and HBV replication is still unclear. In the present study, miR-146a was upregulated in HBV-expressing HepG2.2.15 cells compared with HepG2 cells. Overexpression of miR-146a or knockdown of Zinc finger E-box-binding homeobox 2 (ZEB2) promoted HBV replication and expression, while downregulation of miR-146a or overexpression of ZEB2 suppressed HBV replication and expression. In addition, miR-146a was demonstrated to directly target ZEB2. Furthermore, ZEB2 silencing abated anti-miR-146a-induced inhibition on HBV replication and expression. These findings suggested that miR-146a promoted HBV replication by targeting ZEB2, providing a new antiviral strategy for HBV infection.

Establishment of Cre-mediated HBV recombinant cccDNA (rcccDNA) cell line for cccDNA biology and antiviral screening assays

Hepatitis B virus (HBV) covalently closed circular DNA (cccDNA), existing in hepatocyte nuclei as a stable minichromosome, plays a central role in the life cycle of the virus and permits the persistence of infection. Despite being essential for HBV infection, little is known about the molecular mechanisms of cccDNA formation, regulation and degradation, and there is no therapeutic agents directly targeting cccDNA, fore mostly due to the lack of robust, reliable and quantifiable HBV cccDNA models. In this study, combined the Cre/loxP and sleeping beauty transposons system, we established HepG2-derived cell lines integrated with 2-60 copies of monomeric HBV genome flanked by loxP sites (HepG2-HBV/loxP). After Cre expression via adenoviral transduction, 3.3-kb recombinant cccDNA (rcccDNA) bearing a chimeric intron can be produced in the nuclei of these HepG2-HBV/loxP cells. The rcccDNA could be accurately quantified by quantitative PCR using specific primers and cccDNA pool generated in this model could be easily detected by Southern blotting using the digoxigenin probe system. We demonstrated that the rcccDNA was epigenetically organized as the natural minichromosome and served as the template supporting pgRNA transcription and viral replication. As the expression of HBV S antigen (HBsAg) is dependent on the newly generated cccDNA, HBsAg is the surrogate marker of cccDNA. Additionally, the efficacies of 3 classes of anti-HBV agents were evaluated in HepG2-HBV/loxP cells and antiviral activities with different mechanisms were confirmed. These data collectively suggested that HepG2-HBV/loxP cell system will be powerful platform for studying cccDNA related biological mechanisms and developing novel cccDNA targeting drugs.

Modulators of HBV capsid assembly as an approach to treating hepatitis B virus infection

The search for a cure for hepatitis B virus infection extends beyond interferon and the existing polymerase inhibitors, and targets different aspects of the virus life cycle to develop agents that operate by alternative mechanisms. Examples of small molecules that disrupt the encapsidation of pgRNA have been known for some time, but recent advances in the understanding of nucleocapsid formation, how compounds interact with core protein, and the development of drug-like molecules have recently progressed the study of capsid assembly modulators to proof of concept in the clinic with respect to reduction of viral load in chronic HBV patients. Interference with HBV capsid assembly is thus a legitimate approach to treating HBV infection.

MicroRNA-939 restricts Hepatitis B virus by targeting Jmjd3-mediated and C/EBPα-coordinated chromatin remodeling

Multi-layered mechanisms of virus host interaction exist for chronic hepatitis B virus (HBV) infection, which have been typically manifested at the microRNA level. Our previous study suggested that miRNA-939 (miR-939) may play a potential role in regulating HBV replication. Here we further investigated the mechanism by which miR-939 regulates HBV life cycle. We found that miR-939 inhibited the abundance of viral RNAs without direct miRNA-mRNA base pairing, but via host factors. Expression profiling and functional validation identified Jmjd3 as a target responsible for miR-939 induced anti-HBV effect. Jmjd3 appeared to enhance the transcription efficiency of HBV enhancer II/core promoter (En II) in a C/EBPα-dependent manner. However, the demethylase activity of Jmjd3 was not required in this process. Rather, Jmjd3’s transactivation activity depended on its interaction with C/EBPα. This coordinated action further recruited the Brm containing SWI/SNF chromatin remodeling complex which promoted the transcription of HBV RNAs. Taken together, we propose that the miR-939-Jmjd3 axis perturbs the accessibility of En II promoter to essential nuclear factors (C/EBPα and SWI/SNF complex) therefore leading to compromised viral RNA synthesis and hence restricted viral multiplication.

Hepatitis B virus spliced variants are associated with an impaired response to interferon therapy

During hepatitis B virus (HBV) replication, spliced HBV genomes and splice-generated proteins have been widely described, however, their biological and clinical significance remains to be defined. Here, an elevation of the proportion of HBV spliced variants in the sera of patients with chronic hepatitis B (CHB) is shown to correlate with an impaired respond to interferon-α (IFN-α) therapy. Transfection of the constructs encoding the three most dominant species of spliced variants into cells or ectopic expression of the two major spliced protein including HBSP and N-terminal-truncated viral polymerase protein result in strong suppression of IFN-α signaling transduction, while mutation of the major splicing-related sites of HBV attenuates the viral anti-IFN activities in both cell and mouse models. These results have associated the productions of HBV spliced variants with the failure response to IFN therapy and illuminate a novel mechanism where spliced viral products are employed to resist IFN-mediated host defense.