Alternative methods for validation of cell culture infection with duck hepatitis B virus

Inhibition of duck hepatitis B virus replication by mimic peptides in vitro

The aim of the present study was to investigate the inhibitory effect of specific mimic peptides targeting duck hepatitis B virus polymerase (DHBVP) on duck hepatitis B virus (DHBV) replication in primary duck hepatocytes. Phage display technology (PDT) was used to screen for mimic peptides specifically targeting DHBVP and the associated coding sequences were determined using DNA sequencing. The selected mimic peptides were then used to treat primary duck hepatocytes infected with DHBV in vitro. Infected hepatocytes expressing the mimic peptides intracellularly were also prepared. The cells were divided into mimic peptide groups (EXP groups), an entecavir-treated group (positive control) and a negative control group. The medium was changed every 48 h. Following a 10-day incubation, the cell supernatants were collected. DHBV-DNA in the cellular nucleus, cytoplasm and culture supernatant was analyzed by quantitative polymerase chain reaction (qPCR). Eight mimic peptides were selected following three PDT screening rounds for investigation in the DHBV-infected primary duck hepatocytes. The qPCR results showed that following direct treatment with mimic peptide 2 or 7, intracellular expression of mimic peptide 2 or 7, or treatment with entecavir, the DHBV-DNA levels in the culture supernatant and cytoplasm of duck hepatocytes were significantly lower than those in the negative control (P<0.05). The cytoplasmic DHBV-DNA content of the cells treated with mimic peptide 7 was lower than that in the other groups (P<0.05). In addition, the DHBV-DNA content of the nuclear fractions following the intracellular expression of mimic peptide 7 was significantly lower than that in the other groups (P<0.05). Mimic peptides specifically targeting DHBVP, administered directly or expressed intracellularly, can significantly inhibit DHBV replication in vitro.

Determine the structure of phosphorylated modification of icariin and its antiviral activity against duck hepatitis virus A

BACKGROUND

Our previous research showed that icariin (1) and its phosphorylated structural modification (2) improved the survival and attenuated oxidative stress and liver dysfunction induced by duck virus hepatitis. In this paper, we were one step closer to determine the structure of phosphorylation icariin (2) by the FT-IR, HRESIMS and (13)C NMR. Anti-DHAV activities of 1 and 2 were compared in duck embryonic hepatocytes (DEHs) cultured in vitro and by artificial infection method in vivo. Additionally, the antiviral mechanisms of replication/release in vitro and the DHAV gene expression in vivo of 1 and 2 were analyzed.

RESULTS

Compound 2's molecular formula was C33H42O18P. The results indicated that 1 and 2 effectively resisted DHAV invading DEHs, that they decreased the mortality of ducklings challenged with DHAV, and that 2 performed more effectively. 1 and 2 performed evenly on DHAV release; however, 2 restrained virus replication far more effectively. Since the anti-DHAV mechanisms of 1 and 2 in vitro probably involve suppression of replication and release, 2's better performance in anti-DHAV may result from its far more effectively inhibiting virus replication.

CONCLUSIONS

The compound 2's chemical structure was defined as 8-prenylkaempferol-4'-methylether-3-rhamnosyl-7-(6'''-phosphate)-glycoside. 1 and 2 exhibited anti-virus activity on DHAV. Our results suggest that 1 and 2 might become an anti-virus plant material candidate.

Is hepatitis B-virucidal validation of biocides possible with the use of surrogates?

The hepatitis B virus (HBV) is considered to be a major public health problem worldwide, and a significant number of reports on nosocomial outbreaks of HBV infections have been reported. Prevention of indirect HBV transmission by contaminated objects is only possible through the use of infection-control principles, including the use of chemical biocides, which are proven to render the virus non-infectious. The virucidal activity of biocides against HBV cannot be predicted; therefore, validation of the virucidal action of disinfectants against HBV is essential. However, feasible HBV infectivity assays have not yet been established. Thus, surrogate models have been proposed for testing the efficacy of biocides against HBV. Most of these assays do not correlate with HBV infectivity. Currently, the most promising and feasible assay is the use of the taxonomically related duck hepatitis B virus (DHBV), which belongs to the same Hepadnaviridae virus family. This paper reviews the application of DHBV, which can be propagated in vitro in primary duck embryonic hepatocytes, for the testing of biocides and describes why this model can be used as reliable method to evaluate disinfectants for efficacy against HBV. The susceptibility levels of important biocides, which are often used as ingredients for commercially available disinfectants, are also described.

Comparison of Bush Sophora Root polysaccharide and its sulfate's anti-duck hepatitis A virus activity and mechanism

In order to research the sulfating modification in enhancing the anti-duck hepatitis A virus (DHAV) activity of Bush Sophora Root polysaccharide (BSRPS), sulfated Bush Sophora Root polysaccharide (sBSRPS) was prepared by chlorosulfonic acid-pyridine method. KBr pellets method was applied to analyze their different structures. Anti-DHAV activity was studied by duck embryonic hepatocytes culture in vitro and artificial inoculation method in vivo. Direct immunofluorescence method and Real-time PCR were applied to study the antiviral mechanism of adsorption, replication and release in vitro and the dynamic change of virus content of blood in vivo. The results showed at the most effective content, sBSRPS (7.813 μg/mL) could inhibit both replication and release of DHAV in vitro, BSRPS (500 μg/mL) only inhibit replication. The relative expression of DHAV gene at the 8thh and the mortality rate of sBSRPS group were significantly reduced. These results indicated sBSRPS performed more effectively in anti-DHAV activity than BSRPS.

Estimation of efficiency of solvent-detergent method for virus inactivation in the technology of immunoglobulin production on the model of duck hepatitis B virus

The virucidal action of solvent tributyl phosphate and detergent sodium cholate used in the production of immunoglobulin for inactivation of viruses with lipid envelope was studied on the model of duck hepatitis B virus. PCR analysis revealed no significant decrease in duck hepatitis B virus DNA concentrations after treatment with solvent/detergent. At the same time, in vivo experiments showed that treatment of duck hepatitis B virus with tributyl phosphate (concentration >0.15%) and sodium cholate (concentration >0.1%) at 37°C for 6 h or longer completely inactivated this model virus added to immunoglobulin solution in concentration 5 log ID50. Duck hepatitis B virus appears to be one of the most acceptable model viruses for validation of virus inactivating technologies in manufacturing human plasma preparations.

Development and application of a universal Taqman real-time PCR for quantitation of duck hepatitis B virus DNA

To develop a quantitative assay for universal detection of duck hepatitis B virus (DHBV) DNA, a Taqman real-time fluorescent quantitative polymerase chain reaction (FQ-PCR) assay was developed using primers and probes based on genomic sequences located at nucleotide 241-414 of the DHBV Core region which possesses the highest homology among the 44 DHBV genomes available in Genbank. The DHBV Core gene cloned in pGEM-T was used to generate DHBV DNA standard. The assay had a lowest detection limit of 10(3) copies/ml and a good linear standard curve (Y=-3.989X+49.086, r(2)=0.9993) over a wide range of input DHBV DNA (10(3) to 10(10) copies/ml). The standard deviation of intra- and inter-assay was 0.01-0.06 and 0.05-0.16, respectively, and the coefficient of variation was 1.3-1.8%. The specificity of the assay was validated using duck hepatitis virus type 1, hepatitis B virus, and E. coli DNA. Comparison of ABI 7300 and Bio-Rad iQ5 PCR instruments yielded highly consistent results. The assay showed a positive rate of 63.8% (51/80) DHBV DNA in peripheral blood and liver tissue from ducks from Xi'an, China. The FQ-PCR developed is highly sensitive, specific, reproducible and versatile, and may be used to universally detect DHBV DNA of different DHBV strains.

Does limited virucidal activity of biocides include duck hepatitis B virucidal action?

BACKGROUND

There is agreement that the infectivity assay with the duck hepatitis B virus (DHBV) is a suitable surrogate test to validate disinfectants for hepatitis B virucidal activity. However, since this test is not widely used, information is necessary whether disinfectants with limited virucidal activity also inactivate DHBV. In general, disinfectants with limited virucidal activity are used for skin and sensitive surfaces while agents with full activity are more aggressive. The present study compares the activity of five different biocides against DHBV and the classical test virus for limited virucidal activity, the vaccinia virus strain Lister Elstree (VACV) or the modified vaccinia Ankara strain (MVA).

METHODS

Virucidal assay was performed as suspension test according to the German DVV/RKI guideline. Duck hepatitis B virus obtained from congenitally infected Peking ducks was propagated in primary duck embryonic hepatocytes and was detected by indirect immunofluorescent antigen staining.

RESULTS

The DHBV was inactivated by the use of 40% ethanol within 1-min and 30% isopropanol within 2-min exposure. In comparison, 40% ethanol within 2-min and 40% isopropanol within 1-min exposure were effective against VACV/MVA. These alcohols only have limited virucidal activity, while the following agents have full activity. 0.01% peracetic acid inactivated DHBV within 2 min and a concentration of 0.005% had virucidal efficacy against VACV/MVA within 1 min. After 2-min exposure, 0.05% glutardialdehyde showed a comparable activity against DHBV and VACV/MVA. This is also the case for 0.7% formaldehyde after a contact time of 30 min.

CONCLUSIONS

Duck hepatitis B virus is at least as sensitive to limited virucidal activity as VACV/MVA. Peracetic acid is less effective against DHBV, while the alcohols are less effective against VACV/MVA. It can be expected that in absence of more direct tests the results may be extrapolated to HBV.

In vitro cultivation and cryopreservation of duck embryonic hepatocytes

Hepatitis B-virucidal testing of biocides in quantitative suspension tests using duck hepatitis B virus (DHBV) requires primary duck embryonic hepatocytes for viral propagation. To improve the test system and availability of these cells, commercial culture plates with different growth surfaces were tested for cell cultivation and different approaches for cryopreservation of hepatocyte suspension were examined. After 12 days of culture, the largest amounts of hepatocytes were grown in CellBIND and TTP plates and CellBIND surface showed the lowest tendency of monolayer detachment nearly comparable with collagen 1-coated CELLCOAT plates. For cryopreservation of hepatocyte suspension, the use of growth medium supplemented with fetal calf serum (FCS) and dimethyl sulfoxide (ME(2)SO), FCS supplemented with ME(2)SO or cryosafe-1 as cryoprotective agents provided the highest rates of surviving cells after thawing. The freezing-thawing process did not significantly reduce the susceptibility of hepatocytes to infection with DHBV. In conclusion, plates without collagen 1 such as CellBIND are recommended for cultivation of primary duck embryonic hepatocytes in infectivity experiments of DHBV for virucidal testing of biocides. The use of cryopreserved hepatocytes is possible when freshly isolated cells from the liver of duck embryos are not available.

Cellular chromosome DNA interferes with fluorescence quantitative real-time PCR detection of HBV DNA in culture medium

Fluorescence quantitative real-time PCR (FQ-PCR) is a recently developed technique increasingly used for clinical diagnosis by detection of hepatitis B virus (HBV) DNA in serum. FQ-PCR is also used in scientific research for detection of HBV DNA in cell culture. Understanding potential FQ-PCR interference factors can improve the accuracy of HBV DNA quantification in cell culture medium. HBV positive serum was diluted with culture medium to produce three test groups with HBV DNA levels of 5 x 10(7) copies/ml (high), 5 x 10(5) copies/ml (medium), and 5 x 10(3) copies/ml (low). Chromosome DNA was extracted from HepG2 cells and then added to high, medium, and low group samples at final concentrations of 0, 12.5, 25, 50, and 100 microg/ml. The samples were quantified by FQ-PCR and data were evaluated using statistical software. No marked changes were seen in the quantitative curves for high level HBV DNA samples when the samples were supplemented with 0-100 microg/ml of chromosome DNA. Interference was observed in medium level samples when 50 and 100 microg/ml of chromosome DNA was added. Interference was also observed in low level HBV DNA samples when the concentration of added chromosome DNA was greater than 25 microg/ml. The interference was eliminated when samples were digested by DNase I prior to PCR detection. In Conclusions, the presence of cellular chromosome DNA can interfere with the detection of HBV DNA by FQ-PCR. Removal of cellular chromosome DNA from culture media prior to FQ-PCR is necessary for reliable HBV DNA quantitative detection.

Hexon denaturation of human adenoviruses by different groups of biocides

Human adenoviruses have often been used as surrogates for testing broad-spectrum virucidal efficacy of biocides. However, recent studies have shown that members of this group of viruses have quite different chemical sensitivities and only serotypes 5 and 44 can be recommended as model viruses. In this study, the hexon protein of the serotypes 1, 2, 5, 6 and 8 was exposed to biocides and subsequently detected by western blotting and the RPS Adeno Detector. Only peracetic acid (PAA) at a relatively high concentration of 0.5% led to complete denaturation of hexon protein within 60 min. This effect was uniform for all adenoviruses tested and was not observed after exposure to 0.05-2.5% povidone-iodine (PVP-I) or 0.7% formaldehyde. However, viral infectivity and genome integrity were influenced by PVP-I and formaldehyde and lower concentrations of PAA. In conclusion, the hexon protein of human adenoviruses shows an unexpectedly high and uniform resistance to chemical biocides. The different chemical sensitivities of adenoviruses cannot be explained by the sensitivity of this main structural compound, but the present findings provide new insights into the virucidal action of disinfectants.

Validation of biocides against duck hepatitis B virus as a surrogate virus for human hepatitis B virus

The use of a surrogate virus, namely duck hepatitis B virus (DHBV), has been recommended for testing the virucidal activity of chemical biocides against hepatitis B virus. To date, however, this model has not been recognized as a standard test in European countries, as its laboratory use is associated with considerable difficulties. As previous studies have demonstrated, several alternative procedures may improve the validation of DHBV infection in a cell culture system. Using indirect immunofluorescent antigen staining and the light cycler real-time polymerase chain reaction (PCR) technique, the virucidal activity of peracetic acid (PAA), povidone-iodine (PVP-I) and formaldehyde was tested against DHBV obtained from congenitally infected ducks or prepared from the transfected hepatoma D2 cell line. The results demonstrated that inactivation of DHBV from the D2 cell line was achieved with lower concentrations of the biocides and within shorter exposure time intervals. These lower concentration-exposure time values for DHBV from D2 cells in comparison with DHBV from infected ducks indicated a higher sensitivity of the virus derived from D2 cells. In addition, concentrations of PAA and PVP-I that significantly inactivated DHBV in suspension tests were not able to destroy the viral genome. In conclusion, DHBV from congenitally infected ducks should be used for virucidal testing of chemical biocides against DHBV; DHBV prepared from D2 cells is unsuitable due to its higher sensitivity to biocides. Indirect immunofluorescent staining allows reliable detection of DHBV infectivity, whereas the hepadnavirucidal effect can be evaluated by quantitative PCR.