Efficient inhibition of hepatitis B virus replication by hepatitis delta virus ribozymes delivered by targeting retrovirus

Serological detection of hepatitis B and D virus co-infection among patients attending a tertiary health facility at Maiduguri, Nigeria

Background

Hepatitis D virus (HDV) is highly pathogenic, and clinical studies revealed that HDV infection aggravates the natural history of the underlying hepatitis B virus (HBV) infection by progression to cirrhosis that leads to early decompensation of liver function compared with HBV mono-infection. To determine the seroprevalence of HDV among HBsAg-seropositive patients and associated biochemical profiles at Maiduguri, Nigeria, a hospital-based cross-sectional study on 180 sera of patients positive for HBsAg by ELISA were evaluated for anti-HDV, hepatitis B envelop antigen, anti-HBs antibodies and liver enzyme profiles.

Results

HDV seroprevalence of 3.3% among 180 HBsAg-positive patients. Relatively higher seroprevalence of HDV was observed in males (4.3%) than in females (2.3%). The highest infection rate (20%) was obtained in patients ≥ 56 years. However, no significant association between positive anti-HDV seroprevalence and gender (p > 0.05). Of the 6 (3.3%) anti-HDV-positive patients, only 1 (16.7%) was positive for HBeAg while all were negative for anti-HBs antibodies. The mean level of liver enzyme level of AST and ALT of the anti-HDV-positive patients significantly differ from that of HBsAg mono-infected patients (p ˂ 0.05). However, no significant difference (p < 0.05) between the mean levels of liver enzymes of ALP in anti-HDV-positive and HBsAg mono-infected patients (p ˃ 0.05) was found.

Conclusion

This study revealed a relatively low presence of HDV in HBsAg-positive patients. Furthermore, HDV-HBV co-infected patients had somewhat worse liver enzyme upregulation. This underscores the need for rapid HDV testing and treatment in HBV-infected patients.

Kinetic Parameters of trans Scission by Extended HDV-like Ribozymes and the Prospect for the Discovery of Genomic trans-Cleaving RNAs

Hepatitis delta virus (HDV)-like ribozymes are self-cleaving catalytic RNAs with a widespread distribution in nature and biological roles ranging from self-scission during rolling-circle replication in viroids to co-transcriptional processing of eukaryotic retrotransposons, among others. The ribozymes fold into a double pseudoknot with a common catalytic core motif and highly variable peripheral domains. Like other self-cleaving ribozymes, HDV-like ribozymes can be converted into trans-acting catalytic RNAs by bisecting the self-cleaving variants at non-essential loops. Here we explore the trans-cleaving activity of ribozymes derived from the largest examples of the ribozymes (drz-Agam-2 family), which contain an extended domain between the substrate strand and the rest of the RNA. When this peripheral domain is bisected at its distal end, the substrate strand is recognized through two helices, rather than just one 7 bp helix common among the HDV ribozymes, resulting in stronger binding and increased sequence specificity. Kinetic characterization of the extended trans-cleaving ribozyme revealed an efficient trans-cleaving system with a surprisingly high K_M', supporting a model that includes a recently proposed activation barrier related to the assembly of the catalytically competent ribozyme. The ribozymes also exhibit a very long k_off for the products (∼2 weeks), resulting in a trade-off between sequence specificity and turnover. Finally, structure-based searches for the catalytic cores of these ribozymes in the genome of the mosquito Anopheles gambiae, combined with sequence searches for their putative substrates, revealed two potential ribozyme-substrate pairs that may represent examples of natural trans-cleaving ribozymes.

Dynamics of in vivo hepatitis D virus infection

Hepatitis-D virus (HDV) is a satellite virus of hepatitis-B virus (HBV) whose intracellular products are required for the completion of the HDV life cycle. HDV can replicate in a cell without the presence of HBV but needs hepatitis B surface antigen (HBsAg) to complete virus assembly and packaging. In order to better understand HDV dynamics, we developed a mathematical model and successfully simulated HBV and HDV data under a range of scenarios. Compared to HBV mono-infection, dual HDV infection resulted in lower chronic HBV DNA levels, with more marked suppression for coinfection (1 logs HBV DNA copies/ml lower) compared to superinfection (0.6 logs HBV DNA copies/ml). Although they have no effect on HBV, prenylation inhibitors may provide the best therapy for reducing HDV viremia irrespective of the stage in which they are commenced. We found that highly effective long term pegylated interferon (IFN) therapy (99.99%) eliminates HBV and HDV viremia while less effective long term IFN therapy (99%) will only produce approximately 2.03 logs and no decrease in HBV and HDV viremia respectively in both coinfection and superinfection settings. Our study also suggests that there is a substantial difference in the outcome of therapies depending upon the time of commencement.

CONCLUSION

Mathematical modeling of HDV infection can describe the complex interplay between this virus and HBV. Simulations suggest that HDV impacts on the feedback mechanisms that maintain cccDNA levels and that targeting these mechanisms may result in new therapeutic agents for both viruses.

Hepatitis D Virus Infection Among Hepatitis B Surface Antigen Carriers and in "Isolated anti-HBc" Antibodies Profile in Central Tunisia

BACKGROUND

Hepatitis D Virus (HDV) causes accelerated liver diseases in patients with Hepatitis B Virus (HBV) infection. There is lack of data about its prevalence, related risk factors and interaction with HBV carriers in our country.

OBJECTIVES

The aim of this study was to estimate the prevalence of hepatitis delta and associated risk factors among Hepatitis B surface antigen (HBsAg) and "isolated anti-HBc" profile carriers in central Tunisia.

PATIENTS AND METHODS

In this cross-sectional study, 540 patients with positive HBsAg and 109 "isolated anti-HBc" profile receiving care in a teaching hospital were tested for the presence of HDV serum-markers using commercially available enzyme immunoassay kit. HBV-DNA was detected by nested PCR in "isolated anti-HBc" profile group.

RESULTS

Prevalence of HDV was 8.1% in HBsAg carriers group, but it was significantly higher in active than inactive hepatitis (30.2% and 4.5%, respectively, OR = 9, 95% CI: [4.48-18.58]). There was no significant association between studied risk factors and HDV infection. In the "isolated anti-HBc" profile group, prevalence of HDV was 4.6% and HBV-DNA had negative result in all patients with positive results for HDV.

CONCLUSIONS

Although HDV had low prevalence in our area, it is vital to plan preventive strategies for HDV spread as well as HBV prevention. It is particularly important to suspect HDV infection in active HBV carriers to manage a particularly severe dual infection. HDV infection should be suspected even in negative HBsAg patients having "isolated anti-HBc" profile.

Progress and Prospects of Anti-HBV Gene Therapy Development

Despite the availability of an effective vaccine against hepatitis B virus (HBV), chronic infection with the virus remains a major global health concern. Current drugs against HBV infection are limited by emergence of resistance and rarely achieve complete viral clearance. This has prompted vigorous research on developing better drugs against chronic HBV infection. Advances in understanding the life cycle of HBV and improvements in gene-disabling technologies have been impressive. This has led to development of better HBV infection models and discovery of new drug candidates. Ideally, a regimen against chronic HBV infection should completely eliminate all viral replicative intermediates, especially covalently closed circular DNA (cccDNA). For the past few decades, nucleic acid-based therapy has emerged as an attractive alternative that may result in complete clearance of HBV in infected patients. Several genetic anti-HBV strategies have been developed. The most studied approaches include the use of antisense oligonucleotides, ribozymes, RNA interference effectors and gene editing tools. This review will summarize recent developments and progress made in the use of gene therapy against HBV.

Gene therapeutic approaches to inhibit hepatitis B virus replication

Acute and chronic hepatitis B virus (HBV) infections remain to present a major global health problem. The infection can be associated with acute symptomatic or asymptomatic hepatitis which can cause chronic inflammation of the liver and over years this can lead to cirrhosis and the development of hepatocellular carcinomas. Currently available therapeutics for chronically infected individuals aim at reducing viral replication and to slow down or stop the progression of the disease. Therefore, novel treatment options are needed to efficiently combat and eradicate this disease. Here we provide a state of the art overview of gene therapeutic approaches to inhibit HBV replication. We discuss non-viral and viral approaches which were explored to deliver therapeutic nucleic acids aiming at reducing HBV replication. Types of delivered therapeutic nucleic acids which were studied since many years include antisense oligodeoxynucleotides and antisense RNA, ribozymes and DNAzymes, RNA interference, and external guide sequences. More recently designer nucleases gained increased attention and were exploited to destroy the HBV genome. In addition we mention other strategies to reduce HBV replication based on delivery of DNA encoding dominant negative mutants and DNA vaccination. In combination with available cell culture and animal models for HBV infection, in vitro and in vivo studies can be performed to test efficacy of gene therapeutic approaches. Recent progress but also challenges will be specified and future perspectives will be discussed. This is an exciting time to explore such approaches because recent successes of gene therapeutic strategies in the clinic to treat genetic diseases raise hope to find alternative treatment options for patients chronically infected with HBV.

Prospects for inhibiting the post-transcriptional regulation of gene expression in hepatitis B virus

There is a continuing need for novel antivirals to treat hepatitis B virus (HBV) infection, as it remains a major health problem worldwide. Ideally new classes of antivirals would target multiple steps in the viral lifecycle. In this review, we consider the steps in which HBV RNAs are processed, exported from the nucleus and translated. These are often overlooked steps in the HBV life-cycle. HBV, like retroviruses, incorporates a number of unusual steps in these processes, which use a combination of viral and host cellular machinery. Some of these unusual steps deserve a closer scrutiny. They may provide alternative targets to existing antiviral therapies, which are associated with increasing drug resistance. The RNA post-transcriptional regulatory element identified 20 years ago promotes nucleocytoplasmic export of all unspliced HBV RNAs. There is evidence that inhibition of this step is part of the antiviral action of interferon. Similarly, the structured RNA epsilon element situated at the 5’ end of the polycistronic HBV pregenomic RNA also performs key roles during HBV replication. The pregenomic RNA, which is the template for translation of both the viral core and polymerase proteins, is also encapsidated and used in replication. This complex process, regulated at the epsilon element, also presents an attractive antiviral target. These RNA elements that mediate and regulate gene expression are highly conserved and could be targeted using novel strategies employing RNAi, miRNAs or aptamers. Such approaches targeting these functionally constrained genomic regions should avoid escape mutations. Therefore understanding these regulatory elements, along with providing potential targets, may also facilitate the development of other new classes of antiviral drugs.