Biological characteristics of the rtA181T/sW172* mutant strain of Hepatitis B virus in animal model

Pharmacokinetics and Time-Kill Study of Inhaled Antipseudomonal Bacteriophage Therapy in Mice

Inhaled bacteriophage (phage) therapy is a potential alternative to conventional antibiotic therapy to combat multidrug-resistant (MDR) Pseudomonas aeruginosa infections. However, pharmacokinetics (PK) and pharmacodynamics (PD) of phages are fundamentally different from antibiotics and the lack of understanding potentially limits optimal dosing. The aim of this study was to investigate the in vivo PK and PD profiles of antipseudomonal phage PEV31 delivered by pulmonary route in immune-suppressed mice. BALB/c mice were administered phage PEV31 at doses of 107 and 109 PFU by the intratracheal route. Mice (n = 4) were sacrificed at 0, 1, 2, 4, 8, and 24 h posttreatment and various tissues (lungs, kidney, spleen, and liver), bronchoalveolar lavage fluid, and blood were collected for phage quantification. In a separate study combining phage with bacteria, mice (n = 4) were treated with PEV31 (109 PFU) or phosphate-buffered saline (PBS) at 2 h postinoculation with MDR P. aeruginosa Infective PEV31 and bacteria were enumerated from the lungs. In the phage-only study, the PEV31 titer gradually decreased in the lungs over 24 h, with a half-life of approximately 8 h for both doses. In the presence of bacteria, in contrast, the PEV31 titer increased by almost 2-log10 in the lungs at 16 h. Furthermore, bacterial growth was suppressed in the PEV31-treated group, while the PBS-treated group showed exponential growth. Of the 10 colonies tested, four phage-resistant isolates were observed from the lung homogenates sampled at 24 h after phage treatment. These colonies had a different antibiogram to the parent bacteria. This study provides evidence that pulmonary delivery of phage PEV31 in mice can reduce the MDR bacterial burden.

Hepatitis B virus rtA181T/sW172non-stop mutation may increase resistance fold to adefovir- and entecavir-resistant mutants compared to rtA181T/sW172* mutation

The study aimed to characterize rtA181T/sW172stop (*) and rtA181T/sW172non-stop mutations of hepatitis B virus (HBV). Total of 22,009 patients who visited Beijing 302 Hospital from 2007 to 2016 were enrolled. These patients all received nucleos(t)ide analogues (NAs) treatment and their serum samples were collected for sequence analysis of HBV reverse-transcriptase (RT) and S regions. The rtA181T mutation was detected in 5.37% (1182/22,009) of the patients' samples. The rtA181T-causative sW172*, sW172non-stop (sW172 L/S), and mixed sW172*/non-stop mutations occupied 82.91%, 7.70%, and 9.39%, respectively. The patients with rtA181T/sW172non-stop mutants had a higher HBV DNA level compared to those with rtA181T/sW172* mutants. 44.33% (524/1182) rtA181T-positive samples were detected with signature drug-resistant mutations, including 325 with adefovir-resistant mutation rtA181V/N236T, 57 with lamivudine-resistant mutation rtM204V/I, 99 with entecavir-resistant mutation rtM204V/I plus rt184/202/250 substitution(s), and 43 with multidrug-resistant mutation rtA181V/N236T + rtM204V/I ± rt184/202/250 substitution(s). The rtA181T/sW172non-stop mutation had a higher ratio of coexistence with adefovir-resistant mutation compared to rtA181T/sW172* mutation (42.86% vs. 24.59%, P < 0.05). rtA181T/sW172S + rtN236T and rtA181T/sW172L + rtN236T mutants exhibited higher HBV DNA production and adefovir resistance fold than that of rtA181T/sW172* + rtN236T mutant (98.02% and 85.5% vs. 42.1% in HBV DNA production, and 7.38-fold and 5.49-fold vs. 3.69-fold in half maximal effective concentration of wild-type strain); rtA181T/sW172L + rtS202G + rtM204V strain exhibited higher HBV DNA production and entecavir resistance fold than that of rtA181T/sW172* + rtS202G + rtM204V strain (50.98% vs. 34.49%, 524.00-fold vs. 69.33-fold). In conclusion, rtA181T/sW172non-stop mutation may increase resistance fold of adefovir- and entecavir-resistant mutants compared to rtA181T/sW172* mutation and might influence clinical presentation of NAs-treated patients.

The truncated mutant HBsAg expression increases the tumorigenesis of hepatitis B virus by regulating TGF-β/Smad signaling pathway

Background

It has been reported that the emergence of HBV rtA181T/sW172* mutant could result in a dominant secretion defect of HBsAg and increase the risk of HCC development. This study was designed to reveal the role and possible pathogenic mechanism of truncated mutant HBsAg in tumorigenesis of HBV rtA181T/sW172* mutant.

Results

As compared to wide type or substituted mutant HBsAg, the ratio of cell clones was significant higher in L02 cells stable expressing truncated mutant HBsAg. Injection of L02 cells stable expressing truncated mutant HBsAg into the dorsal skin fold of nude mice resulted in increased primary tumor growth compared to L02 cells stable expressing wide-type and substituted mutant HBsAg. In HBV replication L02 cell lines, the key molecular involved in TGF-β/Smad pathway was also investigated. We found that the mRNA and protein levels of Smad3/2, CREB and CyclinD1 were significantly higher and TGFBI level was significantly lower in cells stably expressing truncated mutant HBsAg as compared to cells stably expressing wide-type and substituted mutant HBsAg. Additionally, after administration of TGF-β1 (increasing TGFBI level), the volume of tumor is obviously reduced in nude mice with injection of L02 cells stable expressing truncated HBsAg.

Conclusions

The emergence of sW172* mutant may increase the tumorigenesis of HBV, and its mechanism may be associated with down-regulated expression of TGFBI in TGF-β/Smad signaling pathway.

Resistance mutations of hepatitis B virus in entecavir-refractory patients

The emergence of resistance mutations in the reverse transcriptase gene of hepatitis B virus (HBV) is associated with treatment failure. Entecavir (ETV) is one of the most potent anti‐HBV reagents; it has a very low resistance rate and is used as the first‐line treatment for chronic hepatitis B. In this study, we isolated HBVs in 4 ETV‐refractory patients (2 with viral breakthrough, 1 with partial virological response, and 1 with flare‐up) and assessed ETV resistance using replication‐competent 1.38‐fold HBV genome‐length molecular clones. The full genome sequences of infected HBVs in ETV‐refractory patients were determined. The HBV molecular clones were generated with the patient‐derived sequences. After transfection of these molecular clones into HepG2 cells, viral replications and ETV susceptibilities were evaluated by measuring the amount of intracellular core‐particle‐associated HBV DNA using Southern blotting and real‐time polymerase chain reaction. Among these cases, ETV‐resistant variants were detected in 2 patients with viral breakthrough and responsible amino acid mutations in reverse transcriptase were successfully identified in these variants. No ETV‐resistant mutation was detected in the other cases. The identified ETV‐resistant mutations did not confer resistance to tenofovir disoproxil fumarate. Conclusion: The HBV replication model with patient‐derived sequences is useful for assessing replication efficiency, susceptibility to anti‐HBV reagents, and responsible resistance mutations and can aid in choosing the appropriate treatment strategy for treatment‐failure cases of chronic hepatitis B. (Hepatology Communications 2017;1:110‐121)

Biological characteristics comparison of HBV rtA181T mutants with truncated or substituted HBsAg expression in vitro and in vivo model systems

The hepatitis B virus(HBV) polymerase rtA181T mutation is selected during long-term antiviral therapy. As the polymerase gene completely overlaps with the envelope (S) gene, HBV rtA181T mutation also carries sW172 mutations. In this study, we investigated whether there were biological differences between rtA181T/sW172* (coding truncated HBsAg) and rtA181T/sW172L (coding substituted HBsAg) mutants. In cell experiments, a slight decline of viral replication was observed in both two mutants as compared to wild-type strains, but the levels of supernatant HBsAg and HBV DNA in rtA181T/sW172* were significantly lower than those in rtA181T/sW172L transfected cells. In animal experiments, we were amazed to find that viral replication in rtA181T/sW172* mutant increased and maintained significantly longer than that in rtA181T/sW172L mutant, while no significant difference was observed between rtA181T/sW172L and wild-type strains. Compared with wild-type strains, there were intracellular accumulations of HBsAg and HBcAg in rtA181/sW172* but none in rtA181/sW172L mutant strains. Importantly, we also found that truncated HBsAg could increase the activity of HBV core promoter, but substituted HBsAg could not. In summary, the characteristics of above two rtA181T mutants mentioned above were significantly different, and it is necessary and important for us to distinguish sW172* truncated mutation from sW172L substituted mutation.

Nucleos(t)ide analogues causes HBV S gene mutations and carcinogenesis

BACKGROUND

The long-term use of nucleos(t)ide analogues causes drug resistance and mutations in the HBV reverse transcriptase (RT) region of the polymerase gene. The RT region overlaps the HBV surface gene (S gene) and therefore, the mutations in the RT region simultaneously modify S gene sequence. Certain mutations in the RT region bring about truncated S proteins because the corresponding changed S gene encodes a stop codon which results in the loss of a large portion of the C-terminal hydrophobic region of HBV surface protein. The rtA181T/sW172*, rtM204I/sW196* and rtV191I/sW182* are the most frequently reported drug-resistant mutations with C-terminal truncation, these mutations have oncogenic potential.

DATA SOURCES

PubMed and Web of Science were searched using terms: "hepatitis B virus", "HBV drug resistance mutation", "HBV surface protein", "HBV truncation", "hepatocellular carcinoma", "rtA181T/sW172*", "rtM204I/sW196*", "rtV191I/sW182*", and relevant articles published in English in the past decades were reviewed.

RESULTS

The rtA181T/sW172* and rtV191I/sW182* mutants occurred more frequently than the rtM204I/sW196* mutant both in chronic hepatitis B patients and the HBV-related hepatocellular carcinoma tissues. Although these mutations occur naturally, nucleos(t)ide analogues therapy is the main driving force. These mutations may exist alone or coexist with other HBV mutations. All these three mutants impair the virion secretion and result in HBV surface protein retention and serum HBV DNA level reduction. These mutations possess potential carcinogenic properties. The three mutations are resistant to more than one nucleos(t)ide analogue and therefore, it is difficult to treat the patients with the truncated mutations.

CONCLUSIONS

Nucleos(t)ide analogues induce drug resistance and HBV S gene truncated mutations. These mutations have potential carcinogenesis.

TAGLN2, a novel regulator involved in Hepatitis B virus transcription and replication

Hepatitis B virus (HBV) infection is one of the major health problems in the world. Transgelin-2 (TAGLN2) expression has been revealed to be significantly altered in previous studies concerning HBV-host interaction. The present study investigated TAGLN2 expression patterns in HBV related hepatocellular carcinoma (HCC) tissues and its role in HBV transcription and replication. We collected 59 HBV related HCC tissue samples, their adjacent non-tumoral tissues and 16 normal livers to make the tissue microarray. TAGLN2 protein was detected by immunohistochemistry and the transcriptional levels of TAGLN2, HBc, HBs and HBx were detected by qRT-PCR. Then we investigated the function of TAGLN2 on HBV transcription and replication in vitro by ectopic expressing or knocking down TAGLN2 in HepG2 and HepG2.2.15 cell lines. We further studied the effect of HBx on TAGLN2 expression with a Tet-on HBx expressing cell line. TAGLN2 protein expression was lower in normal livers and HBV-HCC tissues comparing to adjacent non-tumoral tissues. The transcriptional levels of TAGLN2 in HBV-HCC tissues and their adjacent tissues were positively related to that of HBc, HBs and HBx (P < 0.05). Ectopic expression of TAGLN2 in vitro could enhance HBV transcription and replication while suppressing TAGLN2 had the contrary effect. TAGLN2 could be induced by HBx in a dose-dependent manner. Our data demonstrated that TAGLN2 might be an HBx induced positive host factor involved in HBV transcription and replication and HBx related liver fibrosis and tumorigenesis.

Biological characteristics of the A1762T/G1764A mutant strain of hepatitis B virus in vivo

The double nucleotide, A1762T and G1764A exchange (TA mutation), in the hepatitis B virus (HBV) genome basal core promoter (BCP) region is a common viral mutation in patients with chronic HBV infection. This mutation is located in the binding site of hepatocyte nuclear factor 4 (HNF4), and a number of liver‑enriched transcription factors are involved in the regulation of HBV transcription and replication. The aim of the present study was to investigate the biological characteristics of the HBV strain with this mutation, and the effect of HNF4 inhibition on the replication of this strain in vivo. The results indicated that in vivo the HBV strain with the TA mutation supported a higher level of pregenomic RNA transcription and HBV DNA replication, compared with the wild‑type strain. Furthermore, the concentration of serum HBeAg in the TA mutant group was lower than that in the wild‑type strain. Following treatment of the mice with entecavir (ETV) or tenofovir disoproxil fumarate (TDF), the transcription and replication levels of wild‑type and mutant strains were reduced. In the groups treated with TDF, the inhibition effect was more marked. In hepatocytes in which HNF4 expression was specifically inhibited, the level of 3.5 kb mRNA of HBV was reduced compared with that in mouse cells with normal HNF4 expression, and HBV DNA replication levels were also reduced to a greater extent. Furthermore, following liver‑specific knockdown of HNF4, the reduction in variant virus expression was greater than that of the wild‑type virus. In conclusion, the replication capacity of HBV with the TA mutation was increased, and the mutation was associated with a reduction in serum HBeAg levels. This mutant strain remained sensitive to ETV and TDF, and HNF4 supported a higher replication level of TA mutant HBV in vivo.

The impact of the hepatitis B virus polymerase rtA181T mutation on replication and drug resistance is potentially affected by overlapping changes in surface gene

The emergence of drug-resistant hepatitis B virus (HBV) is a major problem for antiviral treatment in chronic hepatitis B infection. In this study, we analyzed the evolution of drug-resistant mutations and characterized the effects of the rtA181T and rtI233V mutations on viral replication and drug resistance. We performed a clonal analysis of the HBV polymerase gene from serum samples during viral breakthrough treated with antiviral agents. A series of mutant clones containing rtA181T and/or rtI233V mutations were constructed and determined the effect of these mutations on the replication ability and drug resistance. An in vitro study revealed that the effect of the rtA181T mutation on viral replication and drug resistance is dependent on the mutations in the overlapping surface gene. Compared to the rtA181T surface missense mutation (rtA181T/sW172S), the introduction of rtA181T surface nonsense mutation (rtA181T/sW172*) resulted in decreased viral replication and increased drug resistance. Complementation assay revealed that the truncated PreS1 is responsible for reduced replication of rtA181T/sW172* mutant. Moreover, the rtA181T/sW172* mutant exhibited a defect in viral particle secretion. The rtI233V mutation that emerged during adefovir therapy reduced viral replication and conferred resistance to adefovir. Our data suggest that the impact of the rtA181T mutation on replication and drug resistance differs based on the mutation status of the corresponding surface gene. The rtI233V mutation also affects replication ability and drug resistance. This observation suggests the need for genotypic analysis of overlapping surface genes to manage antiviral drug resistance if clinical isolates harbor the rtA181T mutation.

IMPORTANCE

The emergence of drug-resistant HBV that are no longer susceptible to nucleos(t)ide analogues is a major problem for antiviral treatment in chronic hepatitis B infection. Among drug-resistant mutations, the single rtA181T mutation is known to confer cross-resistance to antiviral drugs. This mutation causes intermediate or reduced susceptibility to tenofovir. Moreover, the clinical occurrence of the rtA181T mutation during antiviral therapy is also high. Our study revealed that the effect of the rtA181T mutation on viral replication and drug resistance is dependent on the mutations in the overlapping surface gene. This observation suggests the need for genotypic analysis of overlapping surface genes to manage antiviral drug resistance if clinical isolates harbor the rtA181T mutation. We believe that our study will not only extend the understanding of the drug resistance mechanism, but it will also ultimately provide new treatment options for patients with multidrug resistant HBV.

Hepatitis B virus-induced hepatocellular carcinoma

Many factors are considered to contribute to hepatitis B virus (HBV) associated hepatocellular carcinoma (HCC), including products of HBV, HBV integration and mutation, and host susceptibility. HBV X protein (HBx) can interfere with several signal pathways that associated with cell proliferation and apoptosis, and the impact of HBx C-terminal truncation in the development of HCC has been implicated. Recent studies by advanced sequencing technologies have revealed recurrent HBV DNA integration sites in hepatoma cells and susceptible genes/SNPs play an important role in the pathogenesis of liver cancer. Epigenetic changes, immune and inflammatory factors are also important contributing factors for liver cancer. This mini-review provides an overview on the recent development of HBV induced HCC.