A sequential histologic and immunohistochemical study of duck hepatitis B virus infection in Pekin ducks

Applications of next-generation sequencing analysis for the detection of hepatocellular carcinoma-associated hepatitis B virus mutations

BACKGROUND

Next-generation sequencing (NGS) is a powerful and high-throughput method for the detection of viral mutations. This article provides a brief overview about optimization of NGS analysis for hepatocellular carcinoma (HCC)-associated hepatitis B virus (HBV) mutations, and hepatocarcinogenesis of relevant mutations.

MAIN BODY

For the application of NGS analysis in the genome of HBV, four noteworthy steps were discovered in testing. First, a sample-specific reference sequence was the most effective mapping reference for NGS. Second, elongating the end of reference sequence improved mapping performance at the end of the genome. Third, resetting the origin of mapping reference sequence could probed deletion mutations and variants at a certain location with common mutations. Fourth, using a platform-specific cut-off value to distinguish authentic minority variants from technical artifacts was found to be highly effective. One hundred and sixty-seven HBV single nucleotide variants (SNVs) were found to be studied previously through a systematic literature review, and 12 SNVs were determined to be associated with HCC by meta-analysis. From comprehensive research using a HBV genome-wide NGS analysis, 60 NGS-defined HCC-associated SNVs with their pathogenic frequencies were identified, with 19 reported previously. All the 12 HCC-associated SNVs proved by meta-analysis were confirmed by NGS analysis, except for C1766T and T1768A which were mainly expressed in genotypes A and D, but including the subgroup analysis of A1762T. In the 41 novel NGS-defined HCC-associated SNVs, 31.7% (13/41) had cut-off values of SNV frequency lower than 20%. This showed that NGS could be used to detect HCC-associated SNVs with low SNV frequency. Most SNV II (the minor strains in the majority of non-HCC patients) had either low (< 20%) or high (> 80%) SNV frequencies in HCC patients, a characteristic U-shaped distribution pattern. The cut-off values of SNV frequency for HCC-associated SNVs represent their pathogenic frequencies. The pathogenic frequencies of HCC-associated SNV II also showed a U-shaped distribution. Hepatocarcinogenesis induced by HBV mutated proteins through cellular pathways was reviewed.

CONCLUSION

NGS analysis is useful to discover novel HCC-associated HBV SNVs, especially those with low SNV frequency. The hepatocarcinogenetic mechanisms of novel HCC-associated HBV SNVs defined by NGS analysis deserve further investigation.

Genetic characterization of hepadnaviruses associated with histopathological changes in the liver of duck and goose embryos

Avian hepadnaviruses are etiological agents of hepatitis B, that has been identified primarily in ducks, and more recently in various avian species. In this paper, 16 hepadnaviruses were detected by polymerase chain reaction (PCR) in the field samples from dead embryos of commercially reared domestic duck and goose. Based on the molecular analysis of the S-protein gene sequences and phylogenetic Neighbor-joining tree, identified viruses were clustered in the same genetic group, indicating no host-related diversity. Both duck and goose-origin hepadnaviruses were grouped within the cluster consisting of "Western-country" and "Chinese" duck hepatitis B (DHBV) isolates, showing more evolutionary distances with other known avian hepadnaviruses. Histopathologically, the lesions observed in the liver tissue from hepadnavirus positive duck and goose embryos varied from low to mild degree of perivascular mononuclear cells and mixed cell infiltrations, followed by mild vacuolar changes. Small focal necrotic changes in the liver parenchyma, and bile ductular proliferation were also found in examined liver samples. Generally, the microscopic findings resemble those described in experimentally infected ducks, while this was the first description of hepadnavirus associated lesions in domestic goose. Although hepadnaviruses are considered to have a very narrow host range, this study showed that domestic ducks and geese are susceptible to infection with genetically almost identical hepadnaviruses, that were likely to produce similar microscopic changes in the liver of both duck and goose embryos. The impact of naturally occurred hepadnavirus infection and possible synergistic interactions with other infectious or non-infectious agents on embryo viability needs further investigation.

Antiviral effects of PNA in duck hepatitis B virus infection model

AIM

To study the efficacy of antiviral treatment with PNA for the duck model of HBV (DHBV)-infected ducks. PNA is a 2-amine-9-(2,3-dideoxy-2,3-dihydro-beta-D-arabinofuranosyl)-6-methoxy-9H-purine.

METHODS

The Sichuan Mallard ducklings in the hepatitis B virus model were treated with PNA, a new antiviral agent. DHBV DNA from the blood serum and liver tissues were measured at 0, 5, and 10 d during the treatment and at 3 d withdrawal by real-time PCR. The duck hepatitis B surface antigen (DHBsAg) in the liver cells was observed by Immunohistochemistry (IHC). Pathological changes in the liver tissues were also observed. Control group I was administered with distilled water and control group II was administered with 3-thiacytidine. Treatment group I was administered with PNA at a dose of 40 mg/kg and treatment group II was administered perorally (po) with PNA at a dose of 80 mg/kg. Treatment group III was administered with PNA at a dose of 20 mg/kg and treatment group IV was intravenously administered with PNA at a dose of 40 mg/kg. Each group contained 15 ducklings.

RESULTS

PNA can significantly lower the DHBV replication levels in serum and liver. Compared with control group II, there were no significant differences in inhibiting efficacy in treatment groups I and III (P>0.05) and there were significant differences in inhibiting efficacy in treatment groups II and IV (P<0.05). Interestingly, significant differences were observed at 3 d withdrawal. The DHBV replication levels in each group slightly increased at 3 d withdrawal, but rebounded slightly in the PNA treatment groups than in control group II (P<0.05). The DHBV replication levels in the treatment groups were lower than in control group I. The DHBV replication levels in sera had a positive relationship with that in the liver, but the DHBV replication levels in the liver was lower than that in sera. Pathological changes in the treatment groups were obviously improved and the changes were associated with liver viral DNA levels.

CONCLUSION

The results demonstrate that PNA is a strong inhibitor of DHBV replication in the DHBV-infected duck model.

The woodchuck model of hepatitis B virus infection

The woodchuck hepatitis virus (WHV) was the first of the mammalian and avian hepadnaviruses described after discovery of the virus of hepatitis B (HBV). Woodchucks chronically infected with WHV develop progressively severe hepatitis and hepatocellular carcinoma, which present as lesions that are remarkably similar to those associated with HBV infection in humans. The initial virological studies and studies of pathogenesis utilized woodchucks that had been trapped in the wild and had acquired WHV infection naturally. Research with wild woodchucks was complicated by lack of knowledge of their backgrounds (e.g., dietary history, exposure to parasites or environmental toxins, and source and duration of WHV infection). Breeding colonies of woodchucks have been established and maintained in laboratory animal facilities, and laboratory-reared woodchucks are superior for experimental studies of pathogenesis or hepatocarcinogenesis. It is possible to infect neonatal woodchucks born in the laboratory with standardized inocula and produce a high rate of chronic WHV carriers that are useful for controlled investigations. WHV has been shown experimentally to cause hepatocellular carcinoma, supporting conclusions based on epidemiological and molecular virological studies that HBV is an important etiological factor in human hepatocarcinogenesis. Chronic WHV carrier woodchucks have become a valuable animal model for the preclinical evaluation of antiviral therapy for HBV infection, providing useful pharmacokinetic and pharmacodynamic results in a relevant animal disease model. It also has been shown that the pattern of toxicity and hepatic injury observed in woodchucks treated with certain fluorinated pyrimidines is remarkably similar to that observed in humans that were treated with the same drugs, suggesting the woodchuck has significant potential for the preclincial assessment of antiviral drug toxicity.

Animal models of hepadnavirus-associated hepatocellular carcinoma

Animal models of hepatitis B virus infection have been valuable for determining the mechanisms of hepadnavirus replication, for studies of pathogenesis, and for investigations of viral hepatocarcinogenesis. The woodchuck model also seems to be useful in the discovery and development of antiviral drugs to treat HBV infection and for testing new forms of immunotherapy. In particular, the woodchuck seems to be ideal for studying the effect of antiviral treatment and immunotherapy on the outcome of hepadnavirus infection and on survival. The median life expectancy of experimentally infected, chronic WHV carriers is approximately 29 months, and almost all develop HCC. New types of prophylaxis or therapy can be evaluated under controlled experimental conditions, in a relevant animal model, and within a reasonable time frame.

Treatment of duck hepatitis B virus by antisense poly-2'-O-(2,4-dinitrophenyl)-oligoribonucleotides

The poly-2'-O-(2,4-dinitrophenyl)-oligoribonucleotide (poly-DNP-RNA) with antisense sequence 5'ggguguauggaaaagccguc-3' was designed to target the sequence 2468-2487 in the polymerase gene of duck hepatitis B virus (DHBV). The stereochemically pure RNA was synthesized by using T7 RNA polymerase with synthetic DNA template and subsequently derivatized with 2,4-dinitrofluorobenzene in mild basic conditions to make the poly-DNP-RNA with an average DNP/base ratio of 0.7. In vitro studies showed that this antisense poly-DNP-RNA can hybridize with sense DNA and has high resistance to RNase A digestion. These poly-DNP-RNA were also found to be potent sequence-independent inhibitors of the reverse transcriptase activity of DHBV DNA-polymerase. For in vivo studies, DHBV-infected ducks were treated with antisense, sense, and random noncomplementary sequence poly-DNP-RNA, respectively. The data showed that the antisense poly-DNP-RNA completely inhibited the duck viremia in all nine ducks that had been treated with a dose of 1 mg/kg (i.v.) per day for 25 days. The viremia did not come back after 10 months recession. In the sense group, three of the four ducks showed no inhibition, and in the random group, both ducks maintained their viremia. After 45 days of treatment with the antisense poly-DNP-RNA, followed by 2 weeks of recession, PCR as well as QC-PCR assay and microscopic examination showed that viral DNA had disappeared in liver and that the histology of the damaged liver (filled with fat granules) had returned to normal.

Characterization of age- and dose-related outcomes of duck hepatitis B virus infection

Experimental inoculation of naive ducks with duck hepatitis B virus (DHBV) can lead to one of three outcomes, namely, persistent viremia, transient infection with or without viremia, or no evidence of infection. The ability of individual ducks to resolve DHBV infection was found to be linked to the age of the duck at the time of inoculation and the dose of inoculated virus. (1) In recently hatched ducks inoculated intravenously (i.v.) with 4 x 10(4) DHBV DNA genomes, a switch from persistent viremia to transient antibody appearance was seen at an age of inoculation between 7 and 14 days. A 25-fold increase in the dose of virus (1 x 10(6) DHBV genomes) delayed this switch by 7 days. (2) When 4-month-old ducks were inoculated i.v. with different doses of virus, only those receiving the highest dose (2 x 10(11) DHBV genomes) showed viremia and extensive viral replication and histological changes in the liver; 2/3 ducks in this group had a transient infection, while the third duck had viral replication and histological changes in the liver that were still present at day 120 postinoculation (p.i.). In all ducks receiving lower doses (1 x 10(3), 1 x 10(6), 1 x 10(9) DHBV genomes) antibodies to viral surface and core antigens developed without detectable viral replication in the liver on days 6, 9, or 12 p.i. (3) When 10- to 16-month-old ducks were inoculated i.v. with 2 x 10(11) DHBV genomes, all showed extensive viral replication in hepatocytes and mild to moderate histological changes in the liver on days 4 or 6 p.i. In 4/5 ducks viremia was not detected, anti-surface antibodies were first detected on day 8 p.i., and viral DNA and antigen were cleared from the liver by days 35-47 p.i. The remaining duck became viremic with persistence of virus in the liver until at least day 46 p.i. The findings of the study are consistent with a model for noncytopathic viruses (R. M. Zinkernagel (1996) Science 271, 173-178).

In vivo antiviral activity and pharmacokinetics of (-)-cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine in woodchuck hepatitis virus-infected woodchucks

The (-) enantiomer of cis-5-fluoro-1l-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine [(-)-FTC)], a substituted oxathiolane compound with anti-hepatitis B virus activity in vitro, was assessed for its efficacy in woodchucks with naturally acquired woodchuck hepatitis virus (WHV) infection. Pharmacokinetics and in vitro anabolism were also determined. (-)-FTC was anabolized to the 5'-triphosphate in a dose-related fashion, reaching a maximum concentration at about 24 h in cultured woodchuck hepatocytes. Following administration of a dose of 10 mg/kg of body weight intraperitoneally (i.p.), the clearance of (-)-FTC from plasma was monoexponential, the terminal half-life was 3.76 +/- 1.4 h, and the systemic clearance was 0.12 +/- 0.06 liters/h/kg. The antiviral efficacy of (-)-FTC in the woodchuck model was assessed by quantitation of serum WHV DNA levels and by WHV particle-associated DNA polymerase activity at two dosages, 30 and 20 mg/kg given i.p. twice daily (b.i.d.), respectively. The level of WHV DNA in serum was reduced 20- to 150-fold (average, 56-fold) in the 30-mg/kg-b.i.d. treatment group and 6- to 49-fold (average, 27-fold) in the 20-mg/kg-b.i.d. treatment group. Viral DNA polymerase levels diminished accordingly. One week after treatment was discontinued, WHV levels returned to pretreatment levels in both studies. These animals were biopsied before and following treatment with 30 mg of (-)-FTC per kg. Their livers were characterized by a mild increase in cytoplasmic lipid levels, but this change was not associated with altered liver enzyme levels. Serum chemistry and hematology results were within the normal ranges for all treated animals. We conclude that (-)-FTC is a potent antihepadnaviral agent and that it has no detectable toxic effects in woodchucks when given for up to 25 days. Further development of (-)-FTC as an anti-hepatitis B virus therapy for patients is warranted.

Alterations in intrahepatic expression of duck hepatitis B viral markers with ganciclovir chemotherapy

Ducks congenitally infected with duck hepatitis B virus (DHBV) were treated with the guanosine analogue, ganciclovir, and the effect on serum and intrahepatic expression of DHBV DNA and viral proteins was examined. After 21 days of ganciclovir treatment, a substantial reduction in viraemia occurred; in contrast, the level of circulating DHBV surface antigen was unchanged. Ganciclovir therapy also substantially reduced the level of DHBV DNA replicative intermediates and the expression of viral core and surface antigen in hepatocytes. However, despite the antiviral treatment some liver cells, including the bile duct epithelial cells and putative oval cells, maintained their intense staining for the viral proteins. Furthermore, DHBV-infected cells in extrahepatic sites such as the pancreas, kidney and spleen were also unaffected by ganciclovir treatment. These results suggest that monotherapy with nucleoside analogues is unlikely to eliminate chronic hepadnaviral infection, and antiviral programs should be designed to target all cell populations infected by the virus.

HBcAg and HBsAg expression in ductular cells in chronic hepatitis B

The possible involvement of bile duct epithelium (BDE) in chronic hepatitis B was examined by immunohistochemical investigation of HBcAg and HBsAg expression in biliary cells in 47 liver biopsies with both viral antigens detectable in hepatocytes. HBcAg- and HBsAg-positive cells were identified in nine and five cases, respectively, in atypical and occasionally in typical ductules in cases of acute exacerbation, chronic active hepatitis and active cirrhosis. Atypical ductules were usually located in areas of periportal fibrosis and in cirrhotic septa. Liver cell plates expressing viral markers and undergoing ductular transformation (positive reaction of hepatocytes to BDE-specific, wide-spectrum keratin) were also observed in acinar zone 1, at the periphery and within parenchymal nodules in a number of cases. The presence of both viral antigens in atypical ductules in cases of advanced chronic liver disease most probably expresses the persistence of the virus in cells deriving from biliary metaplasia of infected hepatocytes. However, the detection of the virus in a few typical ductules is indicative of a direct viral infection. According to these findings, ductular cells seem to serve as a suitable host for HBV, their genotype permitting viral replication and antigen production.

Characterization of the antiviral effects of 2' carbodeoxyguanosine in ducks chronically infected with duck hepatitis B virus

This study was carried out to evaluate benefits and limitations of long-term therapy of hepatitis B virus infections with a nucleoside analog inhibitor of virus replication. The model we used was the domestic duck chronically infected with duck hepatitis B virus by in ovo infection. 2' Carbodeoxyguanosine was used as an inhibitor of viral DNA synthesis. In all animals examined there was a reduction in virus production during therapy. A dose of 2' carbodeoxyguanosine of 10 micrograms/kg every other day reduced the number of infected hepatocytes from greater than 95% to 25% to 50% in less than 3 mo, whereas a 10-fold higher dose produced a decline to less than 10%. Histological evaluation revealed mild to moderate liver injury in ducks receiving the higher dose of 2' carbodeoxyguanosine, suggesting that disappearance of infected hepatocytes may have been accelerated by a toxic effect of the drug. Drug treatment did not completely eliminate duck hepatitis B virus from any duck, and replication was restored in all hepatocytes within a few weeks to several months after antiviral therapy was terminated. Our results suggest that elimination of a chronic infection with a single inhibitor of replication may be difficult in a host that lacks an antiviral immune response capable of eliminating at least a portion of the infected hepatocytes and of ultimately producing antibodies capable of neutralizing residual virus.

Detection of mammalian and avian hepadnaviruses by the polymerase chain reaction

The hepadnavirus family contains a number of related viruses able to infect a variety of animal species. In the present study, we have used the polymerase chain reaction and oligonucleotide primers to a conserved region of the viral replicase gene of hepadnaviruses to identify viral sequences in de novo tissues in three well-characterized hepadnavirus systems: the woodchuck, ground squirrel and Pekin duck. We did not detect related hepadnavirus sequences in liver specimens from tree squirrels putatively infected with the tree squirrel hepatitis virus, or in liver specimens from horses with hepatitis (serum sickness), or from dogs with chronic active hepatitis or hepatocellular carcinoma.

Mechanism, kinetics, and role of duck hepatitis B virus e-antigen expression in vivo

No duck hepatitis B virus (DHBV) pre-C transcript has been identified so far, and neither the interrelationship of e-antigen (DHBeAg) with the expression of other viral antigens or virus replication nor its function is known. In this study we identified in infected livers a minor transcript from which the precursor protein of DHBeAg could be synthesized. Mutation of the first AUG on this transcript abolished expression of DHBeAg. DHBV genomes containing this mutation were infectious in Pekin ducks, the kinetics of pre-S envelope protein expression and virus secretion were not significantly different from wild-type, and the mutant genomes did not revert to wild-type to a detectable level after several passages. In contrast to pre-S protein, the level of DHBeAg in the serum was independent of the level of viremia, accumulated gradually to a high and constant level after a lag phase, and was also easily detectable in a mixed infection containing less than 0.1% of wild-type in a pre-C mutant virus containing inoculum. These data indicate that precore protein is synthesized from a minor pre-C mRNA with translation initiation at the pre-C AUG codon, and leads to high levels of DHBeAg rather late in infection. High levels of DHBeAg can even be produced efficiently by a very small subpopulation of wild-type virus in a mixed infection with predominantly pre-C mutant virus. Lack of DHBeAg appears to have no effect on DHBV viability and kinetics of virus secretion into the bloodstream when ducklings are infected with the pre-C AUG mutant virus a few days after birth.

Duck hepatitis B virus infection of non-hepatocytes

One hundred and seventeen ducklings, 42 inoculated with duck hepatitis B virus (DHBV) 2 days after hatching and 55 connatally infected, were studied over a 6-month period in parallel with 20 ducklings without DHBV infection. Using immunohistochemical, in situ and blot hybridization analyses, the natural course of hepatic and extrahepatic infection was examined. DHBV infection started in the liver 2-4 days post-inoculation. There, DHBV was found not only in hepatocytes, but also in bile duct epithelial cells. Further, DHBV infection occurred in exocrine and endocrine pancreas (beginning 6-10 days and 20 days post-inoculation, respectively) and in germinal centers of the spleen (beginning 8 weeks post-inoculation). Occasionally viral DNA was also found in kidney glomeruli. Using strand-specific RNA probes, viral DNA in pancreas and spleen was clearly demonstrated to be replicating intermediates. Hepatic and extrahepatic infection with DHBV was not associated with histologic inflammation or pathologic changes in these tissues or the liver. These data indicate that DHBV can infect cells other than hepatocytes. The biological significance of non-hepatocyte infection for the life-cycle of the virus and its potential significance for viral persistence remain to be determined.