Revival, characterization, and hepatitis B virus infection of cryopreserved human fetal hepatocytes

Liver Organoid Potential Application for Hepatitis E Virus Infection

Despite the advances in hepatitis E virus (HEV) cell infection models' development, HEV infection efficacy in these cell models is still low, which hampers the further study of molecular mechanism of HEV infection and replication and even the interaction between HEV and host. Along with the advances in the technology for liver organoids generation, major efforts will be made to develop liver organoids for HEV infection. Here, we summarize the entire new and impressive cell culture system of liver organoids and discuss their potential application in HEV infection and pathogenesis. Liver organoids can be generated from tissue-resident cells isolated from biopsies of adult tissues or from iPSCs/ESCs differentiation, which can expand the large-scale experiments such as antiviral drug screening. Different types of liver cells working together can recapitulate the liver organ maintaining the physiological and biochemical microenvironments to support cell morphogenesis, migration, and response to viral infections. Efforts to optimize the protocols for liver organoids generation will speed up the research for HEV infection and pathogenesis and even the antiviral drug identification and evaluation.

Establishment and Characterization of an HBV Viral Spread and Infectious System following Long-Term Passage of an HBV Clinical Isolate in the Primary Human Hepatocyte and Fibroblast Coculture System

The existing cell culture-based methods to study hepatitis B virus (HBV) have limitations and do not allow for viral long-term passage. The aim of this study was to develop a robust in vitro long-term viral passage system with optimized cell culture conditions and a viral isolate with the ability to spread and passage. An HBV genotype A clinical isolate was subjected to multiple rounds of UV treatment and passaged in an optimized primary human hepatocyte (PHH)/human fibroblast coculture system. The passaged UV-treated virus was sequenced and further characterized. In addition, a panel of mutant viruses containing different combinations of mutations observed in this virus was investigated. The clinical isolate was passaged for 20 rounds with 21 days per round in an optimized PHH/human fibroblast coculture system while subject to UV mutagenesis. This passaged UV-mutated isolate harbored four mutations: G225A (sR24K) in the S gene, A2062T in the core gene, and two mutations G1764A and C1766T (xV131I) in the basal core promoter (BCP) region. In vitro characterization of the four mutations suggested that the two BCP mutations G1764A and C1766T contributed to the increased viral replication and viral infectivity. A robust in vitro long-term HBV viral passage system has been established by passaging a UV-treated clinical isolate in an optimized PHH/fibroblast coculture system. The two BCP mutations played a key role in the virus's ability to passage. This passage system can be used for studying the entire life cycle of HBV and has the potential for in vitro drug-resistance selection upon further optimization. IMPORTANCE The existing cell culture-based methods to study HBV have limitations and do not allow for viral long-term passage. In this study, an HBV genotype A clinical isolate was subjected to multiple rounds of UV treatment and passaged in an optimized PHH/human fibroblast coculture system. This passaged UV-mutated isolate carried four mutations across the HBV genome, and in vitro characterization of the four mutations suggested that the two basal core promoter (BCP) mutations G1764A and C1766T played a key role in the virus's ability to passage. In summary, we have developed a robust in vitro long-term HBV viral passage system by passaging an UV-treated HBV genotype A clinical isolate in an optimized PHH/human fibroblast coculture system. This passage system can be used for studying the entire life cycle of HBV and has the potential for in vitro drug-resistance selection upon further optimization.

Repurposing of Antazoline Hydrochloride as an Inhibitor of Hepatitis B Virus DNA Secretion

Hepatitis B virus (HBV) belongs to Hepadnaviridae family and mainly infects hepatocytes, which can cause acute or chronic hepatitis. Currently, two types of antiviral drugs are approved for chronic infection clinically: interferons and nucleos(t)ide analogues. However, the clinical cure for chronic infection is still rare, and it is a huge challenge for all researchers to develop high-efficiency, safe, non-tolerant, and low-toxicity anti-HBV drugs. Antazoline hydrochloride is a first-generation antihistamine with anticholinergic properties, and it is commonly used to relieve nasal congestion and in eye drops. Recently, an in vitro high-throughput evaluation system was constructed to screen nearly 800 compounds from the Food and Drug Administration (FDA)-approved Drug Library. We found that arbidol hydrochloride and antazoline hydrochloride can effectively reduce HBV DNA in the extracellular supernatant in a dose-dependent manner, with EC₅₀ of 4.321 μmol/L and 2.910 μmol/L in HepAD38 cells, respectively. Moreover, the antiviral effects and potential mechanism of action of antazoline hydrochloride were studied in different HBV replication systems. The results indicate that antazoline hydrochloride also has a significant inhibitory effect on HBV DNA in the extracellular supernatant of Huh7 cells, with an EC₅₀ of 2.349 μmol/L. These findings provide new ideas for screening and research related to HBV agents.

hNTCP‑expressing primary pig hepatocytes are a valuable tool for investigating hepatitis B virus infection and antiviral drugs

Primary human hepatocytes (PHHs) are the 'gold standard' for investigating hepatitis B virus (HBV) infection and antiviral drugs. However, poor availability, variation between batches and ethical issues regarding PHHs limit their applications. The discovery of human sodium taurocholate co‑transporting polypeptide (hNTCP) as a functional HBV receptor has enabled the development of a surrogate model to supplement the use of PHHs. In the present study, the evolutionary distance of seven species was assessed based on single‑copy homologous genes. Based on the evolutionary distance and availability, PHHs and primary rabbit hepatocytes (PRHs) were isolated and infected with hNTCP‑recombinant lentivirus, and susceptibility to HBV infection in the two cell types was tested and compared. In addition, HBV infection efficiency of hNTCP‑expressing PPHs with pooled HBV‑positive serum and purified particles was determined. The potential use of HBV‑infected hNTCP‑expressing PPHs for drug screening was assessed. The results demonstrated that pigs and rabbits are closer to humans in the divergence tree compared with mice and rats, indicating that pigs and rabbits were more likely to facilitate the HBV post‑entry lifecycle. Following hNTCP complementation and HBV infection, PPHs and Huh7D human hepatocellular carcinoma cells, but not PRHs, exhibited increased hepatitis B surface antigen and hepatitis B e‑antigen secretion, covalently closed circular DNA formation and infectious particle secretion. hNTCP‑expressing PPHs were susceptible to infection with HBV particles purified from pooled HBV‑positive sera, but were poisoned by raw HBV‑positive sera. The use of HBV‑infected hNTCP‑expressing PPHs for viral entry inhibitor screening was revealed to be applicable and reproducible. In conclusion, hNTCP‑expressing PPHs may be valuable tool for investigating HBV infection and antiviral drugs.

Upregulation of HBV transcription by sodium taurocholate cotransporting polypeptide at the postentry step is inhibited by the entry inhibitor Myrcludex B

Sodium taurocholate cotransporting polypeptide (NTCP) is a functional receptor for hepatitis B virus (HBV) entry. However, little is known regarding whether NTCP is involved in regulating the postentry steps of the HBV life cycle. Here, we found that NTCP expression upregulated HBV transcription at the postentry step and that the NTCP-targeting entry inhibitor Myrcludex B (MyrB) effectively suppressed HBV transcription both in an HBV in vitro infection system and in mice hydrodynamically injected with an HBV expression plasmid. Mechanistically, NTCP upregulated HBV transcription via farnesoid X receptor α (FxRα)-mediated activation of the HBV EN2/core promoter at the postentry step in a manner that was dependent on the bile acid (BA)-transport function of NTCP, which was blocked by MyrB. Our findings uncover a novel role for NTCP in the HBV life cycle and provide a reference for the use of novel NTCP-targeting entry inhibitors to suppress HBV infection and replication.

Engineered Livers for Infectious Diseases

Engineered liver systems come in a variety of platform models, from 2-dimensional cocultures of primary human hepatocytes and stem cell-derived progeny, to 3-dimensional organoids and humanized mice. Because of the species-specificity of many human hepatropic pathogens, these engineered systems have been essential tools for biologic discovery and therapeutic agent development in the context of liver-dependent infectious diseases. Although improvement of existing models is always beneficial, and the addition of a robust immune component is a particular need, at present, considerable progress has been made using this combination of research platforms. We highlight advances in the study of hepatitis B and C viruses and malaria-causing Plasmodium falciparum and Plasmodium vivax parasites, and underscore the importance of pairing the most appropriate model system and readout modality with the particular experimental question at hand, without always requiring a platform that recapitulates human physiology in its entirety.

Productive HBV infection of well-differentiated, hNTCP-expressing human hepatoma-derived (Huh7) cells

Feasible and effective cell models for hepatitis B virus (HBV) infection are required for investigating the complete lifecycle of this virus, including the early steps of viral entry. Resistance to dimethyl sulfoxide/polyethylene glycol (DMSO/PEG), hNTCP expression, and a differentiated state are the limiting factors for successful HBV infection models. In the present study, we used a hepatoma cell line (Huh7D^hNTCP) to overcome these limiting factors so that it exhibits excellent susceptibility to HBV infection. To achieve this goal, different hepatoma cell lines were tested with 2.5% DMSO / 4% PEG8000, and one resistant cell line (Huh7D) was used to construct a stable hNTCP-expressing cell line (Huh7D^hNTCP) using a recombinant lentivirus system. Then, the morphological characteristics and differentiation molecular markers of Huh7D^hNTCP cells with or without DMSO treatment were characterized. Finally, the susceptibility of Huh7D^hNTCP cells to HBV infection was assessed. Our results showed that Huh7D cells were resistant to 2.5% DMSO / 4% PEG8000, whereas the others were not. Huh7D^hNTCP cells were established to express a high level of hNTCP compared to liver extracts, and Huh7D^hNTCP cells rapidly transformed into a non-dividing, well-differentiated polarized phenotype under DMSO treatment. Huh7D^hNTCP cells fully supported the entire lifecycle of HBV infection. This cell culture system will be useful for the analysis of host-virus interactions, which should facilitate the discovery of antiviral drugs and vaccines.

Efficient Inhibition of Hepatitis B Virus Infection by a preS1-binding Peptide

Entry inhibitors are promising novel antivirals against hepatitis B virus (HBV) infection. The existing potential entry inhibitors have targeted the cellular receptor(s). In this study, we aim to develop the first entry inhibitor that inhibits HBV infection via targeting viral particles. The preS1 segment of the large envelope glycoprotein of HBV is essential for virion attachment and infection. Previously, we obtained a preS1-binding short peptide B10 by screening a phage display peptide library using the N-terminal half of preS1 (residues 1 to 60, genotype C). We report here that by means of concatenation of B10, we identified a quadruple concatemer 4B10 that displayed a markedly increased preS1-binding activity. The main binding site of 4B10 in preS1 was mapped to the receptor binding enhancing region. 4B10 blocked HBV attachment to hepatic cells and inhibited HBV infection of primary human and tupaia hepatocytes at low nanomolar concentrations. The 4B10-mediated inhibition of HBV infection is specific as it did not inhibit the infection of vesicular stomatitis virus glycoprotein pseudotyped lentivirus or human immunodeficiency virus type 1. Moreover, 4B10 showed no binding activity to hepatic cells. In conclusion, we have identified 4B10 as a promising candidate for a novel class of HBV entry inhibitors.