The earliest steps in hepatitis B virus infection

Research Progress on the Protective Effect of Green Tea Polyphenol (-)-Epigallocatechin-3-Gallate (EGCG) on the Liver

The liver, as the primary metabolic organ, is susceptible to an array of factors that can harm liver cells and give rise to different liver diseases. Epigallocatechin gallate (EGCG), a natural compound found in green tea, exerts numerous beneficial effects on the human body. Notably, EGCG displays antioxidative, antibacterial, antiviral, anti-inflammatory, and anti-tumor properties. This review specifically highlights the pivotal role of EGCG in liver-related diseases, focusing on viral hepatitis, autoimmune hepatitis, fatty liver disease, and hepatocellular carcinoma. EGCG not only inhibits the entry and replication of hepatitis B and C viruses within hepatocytes, but also mitigates hepatocytic damage caused by hepatitis-induced inflammation. Furthermore, EGCG exhibits significant therapeutic potential against hepatocellular carcinoma. Combinatorial use of EGCG and anti-hepatocellular carcinoma drugs enhances the sensitivity of drug-resistant cancer cells to chemotherapeutic agents, leading to improved therapeutic outcomes. Thus, the combination of EGCG and anti-hepatocellular carcinoma drugs holds promise as an effective approach for treating drug-resistant hepatocellular carcinoma. In conclusion, EGCG possesses hepatoprotective properties against various forms of liver damage and emerges as a potential drug candidate for liver diseases.

Mechanical and Electrical Interaction of Biological Membranes with Nanoparticles and Nanostructured Surfaces

In this review paper, we theoretically explain the origin of electrostatic interactions between lipid bilayers and charged solid surfaces using a statistical mechanics approach, where the orientational degree of freedom of lipid head groups and the orientational ordering of the water dipoles are considered. Within the modified Langevin Poisson–Boltzmann model of an electric double layer, we derived an analytical expression for the osmotic pressure between the planar zwitterionic lipid bilayer and charged solid planar surface. We also show that the electrostatic interaction between the zwitterionic lipid head groups of the proximal leaflet and the negatively charged solid surface is accompanied with a more perpendicular average orientation of the lipid head-groups. We further highlight the important role of the surfaces’ nanostructured topography in their interactions with biological material. As an example of nanostructured surfaces, we describe the synthesis of TiO₂ nanotubular and octahedral surfaces by using the electrochemical anodization method and hydrothermal method, respectively. The physical and chemical properties of these nanostructured surfaces are described in order to elucidate the influence of the surface topography and other physical properties on the behavior of human cells adhered to TiO₂ nanostructured surfaces. In the last part of the paper, we theoretically explain the interplay of elastic and adhesive contributions to the adsorption of lipid vesicles on the solid surfaces. We show the numerically predicted shapes of adhered lipid vesicles corresponding to the minimum of the membrane free energy to describe the influence of the vesicle size, bending modulus, and adhesion strength on the adhesion of lipid vesicles on solid charged surfaces.

The structure of a prokaryotic viral envelope protein expands the landscape of membrane fusion proteins

Lipid membrane fusion is an essential function in many biological processes. Detailed mechanisms of membrane fusion and the protein structures involved have been mainly studied in eukaryotic systems, whereas very little is known about membrane fusion in prokaryotes. Haloarchaeal pleomorphic viruses (HRPVs) have a membrane envelope decorated with spikes that are presumed to be responsible for host attachment and membrane fusion. Here we determine atomic structures of the ectodomains of the 57-kDa spike protein VP5 from two related HRPVs revealing a previously unreported V-shaped fold. By Volta phase plate cryo-electron tomography we show that VP5 is monomeric on the viral surface, and we establish the orientation of the molecules with respect to the viral membrane. We also show that the viral membrane fuses with the host cytoplasmic membrane in a process mediated by VP5. This sheds light on protein structures involved in prokaryotic membrane fusion.

Epigallocatechin gallate inhibits hepatitis B virus infection in human liver chimeric mice

BACKGROUND

Persistent hepatitis B virus (HBV) infection causes liver cirrhosis and hepatocellular carcinoma and constitutes a major worldwide health problem. Currently, anti-HBV drugs are limited to peginterferon and nucleos(t)ide analogs, which are costly and have considerable side effects; the development of novel, effective anti-HBV agents is crucial.

METHODS

Catechins are a major group of compounds found in green tea extract and epigallocatechin gallate (EGCG) has been shown to have antiviral properties, including inhibition of cellular entry by HBV. FRG (Fah-/-/ Rag2-/-/ IL-2Rγ/-) mice were used in this study to generate chimeras carrying human primary hepatocytes, to facilitate investigation of the inhibitory effect of EGCG on HBV infection.

RESULTS

Here, we show the inhibitory effect of EGCG on HBV infection and replication in HuS-E/2 cells. The inhibitory effect of EGCG on HBV infection in vivo was confirmed by monitoring HBV DNA and HBsAg in serum and immunostaining the liver tissues of the human liver chimeric mice.

CONCLUSIONS

The effects of EGCG suggest a robust strategy for the treatment of HBV infection and EGCG may have therapeutic potential for the treatment of HBV-associated liver diseases.

Intracellular trafficking of bio-nanocapsule-liposome complex: Identification of fusogenic activity in the pre-S1 region of hepatitis B virus surface antigen L protein

Bio-nanocapsules (BNCs) are a hollow nanoparticle consisting of about 100-nm liposome (LP) embedding about 110 molecules of hepatitis B virus (HBV) surface antigen (HBsAg) L protein as a transmembrane protein. Owing to the human hepatocyte-recognizing domains on the N-terminal region (pre-S1 region), BNCs have recently been shown to attach and enter into human hepatic cells using the early infection mechanism of HBV. Since BNCs could form a complex with an LP containing various drugs and genes, BNC-LP complexes have been used as a human hepatic cell-specific drug and gene-delivery system in vitro and in vivo. However, the role of BNCs in cell entry and intracellular trafficking of payloads in BNC-LP complexes has not been fully elucidated. In this study, we demonstrate that low pH-dependent fusogenic activity resides in the N-terminal part of pre-S1 region (NPLGFFPDHQLDPAFG), of which the first FF residues are essential for the activity, and which facilitates membrane fusion between LPs in vitro. Moreover, BNC-LP complexes can bind human hepatic cells specifically, enter into the cells via clathrin-mediated endocytosis, and release their payloads mostly into the cytoplasm. Taken together, the BNC portion of BNC-LP complexes can induce membrane fusion between LPs and endosomal membranes under low pH conditions, and thereby facilitate the endosomal escape of payloads. Furthermore, the fusogenic domain of the pre-S1 region of HBsAg L protein may play a pivotal role in the intracellular trafficking of not only BNC-LP complexes but also of HBV.

Correlation between pretreatment viral sequences and the emergence of lamivudine resistance in hepatitis B virus infection

The emergence of amino acid or nucleotide substitutions leads to lamivudine resistance in hepatitis B virus (HBV) infected patients. The aim of this study was to investigate whether viral sequences help predict the emergence of lamivudine resistance. The study subjects comprised 59 consecutive patients infected with HBV treated with daily therapy of 100 mg lamivudine. Among those, 32 patients with adequate pretreatment serum preservation were investigated for the correlation between viral amino acid substitutions and the appearance of lamivudine resistance with consideration of clinical background by determining dominant HBV full open reading frames. Viral resistance to lamivudine emerged in 28 of 59 patients (47%) in a median period of 2.45 years. Sequence comparisons of HBV genomes between patients who later developed lamivudine resistance and patients who did not revealed the existence of significant differences between the two groups in the pre-S1 84 (P = 0.042), pre-S2 1 (P = 0.017) and 22 (P = 0.015), and polymerase tp 95 (P = 0.046), judged by a log-rank test. Viral sequence analyses revealed the presence of amino acid substitutions in HBV pre-S1 and pre-S2 that may be associated with the emergence of lamivudine resistance during chronic HBV infection.

Detection of hepatitis B virus PreS1 antigen using a time-resolved fluoroimmunoassay

The hepatitis B virus (HBV) PreS1 antigen is expressed at the distal most region of the envelope protein and contains the hepatocyte receptor-binding site. The presence of the HBV PreS1 antigen in serum and liver of HBsAg-positive patients is a new marker used for diagnosing HBV infection, and is indicative of viral replication. Our objective is to establish a method of time-resolved fluoroimmunoassay (TRFIA) with higher sensitivity and broader detection range for detecting serum HBV PreS1 antigen. Eu(3+) labeling of antibodies was performed with respective labeling kits, and Eu(3+) fluorescence intensity was measured with an auto DELFIA1235 TRFIA analyzer. The established method was evaluated for its performance. Serum specimens (574 in total) from Wuxi People's Hospital were analyzed for PreS1 antigen using the TRFIA and ELISA. The precision, specificity, and sensitivity of the TRFIA were clearly better than ELISA. The detection limit was 0.01 ng/mL. The average recovery rate for PreS1 antigens was 103.3%. There was significant correlation between the PreS1 antigen results obtained by TRFIA and ELISA in 374 serum samples with HBV >10(3) IU/mL (χ(2) = 25.04, p < 0.01) and 183 HbeAg-positive serum samples (χ(2) = 12.07, p < 0.01). Normal reference ranges were established at 0-0.32 ng/mL based on the values obtained from 100 healthy controls. TRFIA is a significantly effective method for clinical detection of serum HBV PreS1 antigens.

DNA-tumor virus entry--from plasma membrane to the nucleus

DNA-tumor viruses comprise enveloped and non-enveloped agents that cause malignancies in a large variety of cell types and tissues by interfering with cell cycle control and immortalization. Those DNA-tumor viruses that replicate in the nucleus use cellular mechanisms to transport their genome and newly synthesized viral proteins into the nucleus. This requires cytoplasmic transport and nuclear import of their genome. Agents that employ this strategy include adenoviruses, hepadnaviruses, herpesviruses, and likely also papillomaviruses, and polyomaviruses, but not poxviruses which replicate in the cytoplasm. Here, we discuss how DNA-tumor viruses enter cells, take advantage of cytoplasmic transport, and import their DNA genome through the nuclear pore complex into the nucleus. Remarkably, nuclear import of incoming genomes does not necessarily follow the same pathways used by the structural proteins of the viruses during the replication and assembly phases of the viral life cycle. Understanding the mechanisms of DNA nuclear import can identify new pathways of cell regulation and anti-viral therapies.

Identification of the critical regions in hepatitis B virus preS required for its stability

As a hepatitis B virus (HBV) envelope domain, preS plays significant roles in receptor recognition and viral infection. However, the regions critical for maintaining a stable and functional conformation of preS are still unclear and require further investigation. In order to unravel these regions, serially truncated fragments of preS were constructed and expressed in Escherichia coli. Their solubility, stability, secondary structure, and affinity to polyclonal antibodies and hepatocytes were examined. The results showed that amino acids 31-36 were vital for its stable conformation, and the absence of 10-36 amino acids significantly reduced its binding to polyclonal antibodies as well as hepatocytes. The most stable fragment 1-120 (preS1 + N-terminal 12 amino acids of preS2), perhaps the core of preS, was discovered, which bound to HepG2 cells most tightly. Moreover, the availability of large amounts of well-folded and stable preS1-120 enables us to carry out further structural determination and mechanistic study on HBV infection.

Overexpression and purification of PreS region of hepatitis B virus antigenic surface protein adr subtype in Escherichia coli

PreS domain of Hepatitis B virus (HBV) surface antigen is a good candidate for an effective vaccine as it activates both B and T cells besides binding to hepatocytes. This report deals with overexpression and purification of adr subtype of surface antigen that is more prevalent in Pakistan. PreS region, comprising 119 aa preS1 region plus a 55 aa preS2 region plus 11 aa from the N-terminal S region, was inserted in pET21a+ vector, cloned in E. coli DH5alpha cells and expressed in E. coli BL21 codon+ cells. The conditions for over expression were optimized using different concentrations of IPTG (0.01-5 mM), and incubating the cells at different temperatures (23-41 degrees C) for different durations (0-6 h). The cells were grown under the given optimized conditions (0.5 mM IPTG concentration at 37 degrees C for 4 h), lysed by sonication and the protein was purified by ion exchange chromatography. On the average, 24.5 mg of recombinant protein was purified per liter of culture. The purified protein was later lyophilized and stored at -80 degrees.

High level of genetic heterogeneity in S and P genes of genotype D hepatitis B virus

The genetic heterogeneity of hepatitis B virus (HBV) genotypes and subgenotypes was investigated by directly sequencing amplified PreS, S and P genes of HBV isolates obtained from the plasma of 99 subjects with chronic HBV infection. Genotype D showed the greatest intragenotypic and intrasubgenotypic divergence: in particular, the a determinant was mutated in 58.2% of the genotype D patients, two of whom showed prototypic vaccine-induced escape mutants at codon 145. Moreover, five sites under significant positive selection were found in the S protein of the D isolates: one in the a determinant and four in the highly hydrophobic C terminal. Our results suggest that careful surveillance of vaccine-induced escape mutants should be considered in populations with highly frequent genotype D infections, and raise questions concerning the possible relationship between the genetic heterogeneity, host immunity and pathogenicity of this HBV genotype.

Identification and characterization of peptides that interact with hepatitis B virus via the putative receptor binding site

A direct involvement of the PreS domain of the hepatitis B virus (HBV) large envelope protein, and in particular amino acid residues 21 to 47, in virus attachment to hepatocytes has been suggested by many previous studies. Several PreS-interacting proteins have been identified. However, they share few common sequence motifs, and a bona fide cellular receptor for HBV remains elusive. In this study, we aimed to identify PreS-interacting motifs and to search for novel HBV-interacting proteins and the long-sought receptor. PreS fusion proteins were used as baits to screen a phage display library of random peptides. A group of PreS-binding peptides were obtained. These peptides could bind to amino acids 21 to 47 of PreS1 and shared a linear motif (W1T2X3W4W5) sufficient for binding specifically to PreS and viral particles. Several human proteins with such a motif were identified through BLAST search. Analysis of their biochemical and structural properties suggested that lipoprotein lipase (LPL), a key enzyme in lipoprotein metabolism, might interact with PreS and HBV particles. The interaction of HBV with LPL was demonstrated by in vitro binding, virus capture, and cell attachment assays. These findings suggest that LPL may play a role in the initiation of HBV infection. Identification of peptides and protein ligands corresponding to LPL that bind to the HBV envelope will offer new therapeutic strategies against HBV infection.

Gamma-adaptin, a novel ubiquitin-interacting adaptor, and Nedd4 ubiquitin ligase control hepatitis B virus maturation

Hepatitis B virus (HBV) budding from infected cells is a tightly regulated process that requires both core and envelope structures. Here we report that HBV uses cellular gamma2-adaptin and Nedd4, possibly in conjunction with ubiquitin, to coordinate its assembly and release. In search of interaction partners of the viral L envelope protein, we previously discovered gamma2-adaptin, a putative endosomal sorting and trafficking adaptor of the adaptor protein complex family. We now demonstrate that the viral core interacts with the same gamma2-adaptor and that disruption of the HBV/gamma2-adaptin interactions inhibits virus production. Mutational analyses revealed a hitherto unknown ubiquitin-binding activity of gamma2-adaptin, specified by a ubiquitin-interacting motif, which contributes to its interaction with core. For core, the lysine residue at position 96, a potential target for ubiquitination, was identified to be essential for both gamma2-adaptin-recognition and virus production. The participation of the cellular ubiquitin system in HBV assembly was further suggested by our finding that core interacts with the endosomal ubiquitin ligase Nedd4, partly via its late domain-like PPAY sequence. Overexpression of a catalytically inactive Nedd4 mutant diminished HBV egress, indicating that protein ubiquitination is functionally involved in virus production. Additional evidence for a link of HBV assembly to the endosomal machinery was provided by immunolabeling studies that demonstrated colocalization of core and L with gamma2-adaptin in compartments positive for the late endosomal marker CD63. Together, these data indicate that an enveloped DNA virus exploits a new ubiquitin receptor together with endosomal pathway functions for egress from hepatocytes.

Expression and purification of the complete PreS region of hepatitis B Virus

AIM: To express the complete PreS region of HBV in E.coli with good solubility and stability, and to establish an effective method for purification of the recombinant PreS protein.

METHODS: The complete PreS region (PreS1 and PreS2) was fused into a series of tags including glutathione S-transferase (GST), dihydrofolate reductase (DHFR), maltose binding protein (MBP), 6×histidine, chitin binding domain (CBD), and thioredoxin, respectively. Expression of recombinant PreS fusion proteins was examined by SDS-PAGE analysis and confirmed by Western blot. Two fusion proteins, thio-PreS, and PreS-CBD, with desirable solubility and stability, were subjected to affinity purification and further characterization.

RESULTS: Recombinant PreS fusion proteins could be synthesized with good yields in E.coli. However, most of these proteins except for thio-PreS and PreS-CBD were vulnerable to degradation or insoluble as revealed by SDS-PAGE and Western blot. Thio-PreS could be purified by affinity chromatography with nickel-chelating sepharose as the matrix. However, some impurities were also co-purified. A simple freeze-thaw treatment yielded most of the thio-PreS proteins in solution while the impurities were in the precipitate. Purified thio-PreS protein was capable of inhibiting the binding of HBV virion to a specific monoclonal antibody against an epitope within the PreS1 domain.

CONCLUSION: Increased solubility and stability of the complete PreS region synthesized in E.coli can be achieved by fusion with the thioredoxin or the CBD tag. A simple yet highly effective method has been established for the purification of the thio-PreS protein. Purified thio-PreS protein likely assumes a native conformation, which makes it an ideal candidate for studying the structure of the PreS region as well as for screening antivirals.

Functional incorporation of green fluorescent protein into hepatitis B virus envelope particles

The envelope of hepatitis B virus (HBV), containing the L, M, and S proteins, is essential for virus entry and maturation. For direct visualization of HBV, we determined whether envelope assembly could accommodate the green fluorescent protein (GFP). While the C-terminal addition of GFP to S trans-dominant negatively inhibited empty envelope particle secretion, the N-terminal GFP fusion to S (GFP.S) was co-integrated into the envelope, giving rise to fluorescent particles. Microscopy and topogenesis analyses demonstrated that the proper intracellular distribution and folding of GFP.S, required for particle export were rescued by interprotein interactions with wild-type S. Thereby, a dual location of GFP, inside and outside the envelope, was observed. GFP.S was also efficiently packaged into the viral envelope, and these GFP-tagged virions retained the capacity for attachment to HBV receptor-positive cells in vitro. Together, GFP-tagged virions should be suitable to monitor HBV uptake and egress in live hepatocytes.

Establishment and assessment of two methods for quantitative detection of serum duck hepatitis B virus DNA

AIM: To establish and assess the methods for quantitative detection of serum duck hepatitis B virus (DHBV) DNA by quantitative membrane hybridization using DHBV DNA probe labeled directly with alkaline phosphatase and fluorescence quantitative PCR (qPCR).

METHODS: Probes of DHBV DNA labeled directly with alkaline phosphatase and chemiluminescent substrate CDP-star were used in this assay. DHBV DNA was detected by autoradiography, and then scanned by DNA dot-blot. In addition, three primers derived from DHBV DNA S gene were designed. Semi-nested primer was labeled by AmpliSensor. Standard curve of the positive standards of DHBV DNA was established after asymmetric preamplification, semi-nested amplification and on-line detection. Results from 100 samples detected separately by alkaline phosphatase direct-labeled DHBV DNA probe with dot-blot hybridization and digoxigenin-labeled DHBV DNA probe hybridization. Seventy samples of duck serum were tested by fluorescent qPCR and digoxigenin-labeled DHBV DNA probe in dot-blot hybridization assay and the correlation of results was analysed.

RESULTS: Sensitivity of alkaline phosphatase direct-labeled DHBV DNA probe was 10 pg. The coincidence was 100% compared with digoxigenin-labeled DHBV DNA probe assay. After 30 cycles, amplification products showed two bands of about 180 bp and 70 bp by 20 g/L agarose gel electrophoresis. Concentration of amplification products was in direct proportion to the initial concentration of positive standards. The detection index was in direct proportion to the quantity of amplification products accumulated in the current cycle. The initial concentration of positive standards was in inverse proportion to the number of cycles needed for enough quantities of amplification products. Correlation coefficient of the results was (0.97, P < 0.01) between fluorescent qPCR and dot-blot hybridization.

CONCLUSION: Alkaline phosphatase direct-labeled DHBV DNA probe in dot-blot hybridization and fluorescent qPCR can be used as valuable means to quantify DHBV DNA in serum.

Establishment of mice model with human viral hepatitis B

AIM: To establish a mice model of hepatitis B by using HBV-transgenic mice, and to transfer HBV-specific cytotoxic T lymphocytes (CTL) induced from syngeneic BALB/c mice immunized by a eukaryotic expression vector containing HBV complete genome DNA.

METHODS: HBV DNA was obtained from digested pBR322-2HBV and ligated with the vector pcDNA3. Recombinant pcDNA3-HBV was identified by restriction endonuclease assay and transfected into human hepatoma cell line HepG2 with lipofectin. ELISA was used to detect the expression of HBsAg in culture supernatant, and RT-PCR to determine the existence of HBV PreS1 mRNA. BALB/c mice were immunized with pcDNA3-HBV or pcDNA3 by intramuscular injection. ELISA was used to detect the expression of HBsAb in serum. MTT assay was used to measure non-specific or specific proliferation ability and specific killing activity of spleen lymphocytes. Lymphocytes from immunized mice were transferred into HBV-transgenic mice (2.5 × 10⁷ per mouse). Forty-eight hours later, the level of serum protein and transaminase was detected with biochemical method, liver and kidney were sectioned and stained by HE to observe the pathological changes.

RESULTS: By enzyme digestion with Eco RI, Xho I and Hind III, the recombinant pcDNA3-HBV was verified to contain a single copy of HBV genome, which was inserted in the positive direction. HepG2 cells transfected with the recombinant could stably express PreS1 mRNA and HBsAg. After immunized by pcDNA3-HBV for 4 weeks, HBsAb was detected in the serum of BALB/c mice. The potential of spleen lymphocytes for both non-specific and specific proliferation and the specific killing activity against target cells were enhanced. The transgenic mice in model group had no significant changes in the level of serum protein but had an obvious increase of ALT and AST. The liver had obvious pathological changes, while the kidney had no evident damage.

CONCLUSION: A eukaryotic expression vector pcDNA3-HBV containing HBV complete genome is constructed successfully. HepG2 cells transfected with the recombinant can express PreS1 mRNA and HBsAg stably. Specific cellular immune response can be induced in mice immunized by pcDNA3-HBV. A mice model of acute hepatitis with HBV has been established.