Chronic hepatitis D-What is changing?

Evaluating protein prenylation of human and viral CaaX sequences using a humanized yeast system

Prenylated proteins are prevalent in eukaryotic biology (∼1-2% of proteins) and are associated with human disease, including cancer, premature aging and infections. Prenylated proteins with a C-terminal CaaX sequence are targeted by CaaX-type prenyltransferases and proteases. To aid investigations of these enzymes and their targets, we developed Saccharomyces cerevisiae strains that express these human enzymes instead of their yeast counterparts. These strains were developed in part to explore human prenyltransferase specificity because of findings that yeast FTase has expanded specificity for sequences deviating from the CaaX consensus (i.e. atypical sequence and length). The humanized yeast strains displayed robust prenyltransferase activity against CaaX sequences derived from human and pathogen proteins containing typical and atypical CaaX sequences. The system also recapitulated prenylation of heterologously expressed human proteins (i.e. HRas and DNAJA2). These results reveal that substrate specificity is conserved for yeast and human farnesyltransferases but is less conserved for type I geranylgeranyltransferases. These yeast systems can be easily adapted for investigating the prenylomes of other organisms and are valuable new tools for helping define the human prenylome, which includes physiologically important proteins for which the CaaX modification status is unknown.

Prevalence of hepatitis D virus infection among patients with chronic hepatitis B infection in a tertiary care centre in Thailand

Knowledge about the epidemiology of hepatitis D virus (HDV) is essential for effective screening and management. Our study aimed to update the prevalence of HDV infection among patients with hepatitis B virus (HBV) infection at hepatology clinics in Thailand. We enrolled HBV-infected patients from hepatology clinics at King Chulalongkorn Memorial Hospital, Bangkok, Thailand, between June 2022 and November 2023. Demographic, biochemical characteristics, and liver-related complications (LRC), including cirrhosis and hepatocellular carcinoma, were reviewed. The competitive enzyme and chemiluminescence immunoassays were used to detect anti-HDV antibodies. Real-time polymerase chain reaction (RT-PCR) was used to test for HDV RNA in anti-HDV-positive patients. The HDV genotype was identified in detectable HDV RNA samples. Of the 702 enrolled patients, four (0.6%) had positive and equivocal for both anti-HDV tests. Two (50.0%) of the four patients tested positive for HDV RNA and genotype 1 was identified; one had multiple risk factors. Anti-HDV seroprevalence was not significantly different between patients with and without LRC. In conclusion, HDV co-infection is less common in Thailand than globally. Additionally, our study identified genotype 1, the predominant HDV genotype worldwide, and observed co-infection even without LRC.

A Humanized Yeast System for Evaluating the Protein Prenylation of a Wide Range of Human and Viral CaaX Sequences

The C-terminal CaaX sequence (cysteine-aliphatic-aliphatic-any of several amino acids) is subject to isoprenylation on the conserved cysteine and is estimated to occur in 1-2% of proteins within yeast and human proteomes. Recently, non-canonical CaaX sequences in addition to shorter and longer length CaX and CaaaX sequences have been identified that can be prenylated. Much of the characterization of prenyltransferases has relied on the yeast system because of its genetic tractability and availability of reporter proteins, such as the a-factor mating pheromone, Ras GTPase, and Ydj1 Hsp40 chaperone. To compare the properties of yeast and human prenyltransferases, including the recently expanded target specificity of yeast farnesyltransferase, we have developed yeast strains that express human farnesyltransferase or geranylgeranyltransferase-I in lieu of their yeast counterparts. The humanized yeast strains display robust prenyltransferase activity that functionally replaces yeast prenyltransferase activity in a wide array of tests, including the prenylation of a wide variety of canonical and non-canonical human CaaX sequences, virus encoded CaaX sequences, non-canonical length sequences, and heterologously expressed human proteins HRas and DNAJA2. These results reveal highly overlapping substrate specificity for yeast and human farnesyltransferase, and mostly overlapping substrate specificity for GGTase-I. This yeast system is a valuable tool for further defining the prenylome of humans and other organisms, identifying proteins for which prenylation status has not yet been determined.

Interferon-based treatment of chronic hepatitis D

Treatment of hepatitis D virus (HDV) infection has been based on the administration of interferon-alfa for more than three decades. First studies to treat HDV-infected patients with type 1 interferons were already performed in the 1980s. Several smaller trials and case series were reported thereafter. During the mid 2000s the use of pegylated interferons for hepatitis D was established. Since then, additional trials were performed in different countries exploring strategies to personalize treatment including extended treatment durations. The overall findings were that about one-quarter to one-third of patients benefit from interferon treatment with persistent suppression of HDV replication. However, only few patients achieve also functional cure of hepatitis B with HBsAg loss. Importantly, several studies indicate that successful interferon treatment is associated with improved clinical long-term outcomes. Still, only a proportion of patients with hepatitis D can be treated with interferons. Even though alternative treatments are currently developed, it is likely that pegylated interferon-alfa will still have an important role in the management of hepatitis D - either alone or in combination. Therefore, better biomarkers are needed to select patients with a high likelihood to benefit from interferon-based treatments. In this review we are discussing basic principles of mode of action of interferon alpha against HDV, summarize previous data on interferon treatment of hepatitis D and give an outlook on potential combinations with novel drugs currently in development.

No Hepatitis Delta Virus Seropositivity among Blood Donors with Overt and Occult Hepatitis B Infection in Dalian, Liaoning Province, China

Hepatitis delta virus (HDV) is an obligate satellite of hepatitis B virus (HBV). Dual HDV/HBV infection is associated with down-regulated HBV replication and fast progression to severe liver disease. Although HDV is transmissible through exposure to infected blood, data about HDV infection in blood donors remain scarce. Between 2011 and 2021, 869,633 donations were collected from prequalified donors in Dalian, China. In total, 1060 (0.12%) were confirmed HBsAg and/or HBV DNA-reactive. Subsequently, anti-HDV IgG was tested in 2175 donations, including 65 that tested HBsAg+ pre donation, 1017 confirmed HBV-positive (507 HBsAg+/HBV DNA+, 33 HBsAg+/DNA-, 477 HBsAg-/DNA+ (451 occult (OBI) and 26 acute infections)), 327 viral DNA non-repeated-reactive, 397 anti-HBc-only, and 369 anti-HBs-only. Two (0.09%) samples tested anti-HDV IgG weakly reactive but were unconfirmed by IgM and IgG repeat testing with alternative assays, suggesting an initial false reactivity. In addition, HDV testing in a subgroup of confirmed OBI donors, comprising 451 donors from Dalian and 126 archived samples of OBI donors from around the world, showed only one non-Chinese donor to be repeatedly anti-HDV-reactive, suggesting that HDV/HBV coinfection does not play a significant role in the genesis of OBI. The overall data suggested an extremely low prevalence of HDV infection among blood donors in Liaoning province, Northeast China.

Delta hepatitis epidemiology and the global burden of disease

Delta Hepatitis is considered the most severe form of hepatitis, with varied prevalence, genotype distribution and risk factors worldwide. Current knowledge of global epidemiology is limited due to variable screening practices for HDV. Here, we summarize what is currently known about the prevalence of testing and prevalence of HDV positivity globally.

Identifying and Screening At-Risk Patients for Hepatitis Delta Virus: A Case Report

Hepatitis Delta Virus (HDV) is associated with one of the most severe forms of viral hepatitis, with rapid progression to cirrhosis and hepatocellular carcinoma. While HDV was thought to be uncommon in the United States, recent data shows that its prevalence may be significantly higher than formerly acknowledged. Early identification of HDV is critical since approved therapeutic options are only available for compensated patients. All patients with a reactive hepatitis B virus surface antigen should undergo HDV screening, especially those with additional risk factors, including migration from an endemic area, immunosuppressed patients, hemodialysis patients, gay and bisexual men, persons who inject drugs, and persons employed in healthcare or public safety professions.

Hepatitis B and Hepatitis D Viruses: A Comprehensive Update with an Immunological Focus

Hepatitis B virus (HBV) and hepatitis delta virus (HDV) are highly prevalent viruses estimated to infect approximately 300 million people and 12-72 million people worldwide, respectively. HDV requires the HBV envelope to establish a successful infection. Concurrent infection with HBV and HDV can result in more severe disease outcomes than infection with HBV alone. These viruses can cause significant hepatic disease, including cirrhosis, fulminant hepatitis, and hepatocellular carcinoma, and represent a significant cause of global mortality. Therefore, a thorough understanding of these viruses and the immune response they generate is essential to enhance disease management. This review includes an overview of the HBV and HDV viruses, including life cycle, structure, natural course of infection, and histopathology. A discussion of the interplay between HDV RNA and HBV DNA during chronic infection is also included. It then discusses characteristics of the immune response with a focus on reactions to the antigenic hepatitis B surface antigen, including small, middle, and large surface antigens. This paper also reviews characteristics of the immune response to the hepatitis D antigen (including small and large antigens), the only protein expressed by hepatitis D. Lastly, we conclude with a discussion of recent therapeutic advances pertaining to these viruses.

What role for cellular metabolism in the control of hepatitis viruses?

Hepatitis B, C and D viruses (HBV, HCV, HDV, respectively) specifically infect human hepatocytes and often establish chronic viral infections of the liver, thus escaping antiviral immunity for years. Like other viruses, hepatitis viruses rely on the cellular machinery to meet their energy and metabolite requirements for replication. Although this was initially considered passive parasitism, studies have shown that hepatitis viruses actively rewire cellular metabolism through molecular interactions with specific enzymes such as glucokinase, the first rate-limiting enzyme of glycolysis. As part of research efforts in the field of immunometabolism, it has also been shown that metabolic changes induced by viruses could have a direct impact on the innate antiviral response. Conversely, detection of viral components by innate immunity receptors not only triggers the activation of the antiviral defense but also induces in-depth metabolic reprogramming that is essential to support immunological functions. Altogether, these complex triangular interactions between viral components, innate immunity and hepatocyte metabolism may explain why chronic hepatitis infections progressively lead to liver inflammation and progression to cirrhosis, fibrosis and hepatocellular carcinoma (HCC). In this manuscript, we first present a global overview of known connections between the innate antiviral response and cellular metabolism. We then report known molecular mechanisms by which hepatitis viruses interfere with cellular metabolism in hepatocytes and discuss potential consequences on the innate immune response. Finally, we present evidence that drugs targeting hepatocyte metabolism could be used as an innovative strategy not only to deprive viruses of key metabolites, but also to restore the innate antiviral response that is necessary to clear infection.

Modeling the Interplay between HDV and HBV in Chronic HDV/HBV Patients

Hepatitis D virus is an infectious subviral agent that can only propagate in people infected with hepatitis B virus. In this study, we modified and further developed a recent model for early hepatitis D virus and hepatitis B virus kinetics to better reproduce hepatitis D virus and hepatitis B virus kinetics measured in infected patients during anti-hepatitis D virus treatment. The analytical solutions were provided to highlight the new features of the modified model. The improved model offered significantly better prospects for modeling hepatitis D virus and hepatitis B virus interactions.