Comparative study of DHBV DNA levels and endogenous DNA polymerase activity in naturally infected ducklings in France

Serial transmission of spongiocytic hepatitis to woodchucks (possible association with a specific delta strain)

BACKGROUND/AIMS

Outbreaks of severe hepatitis have been reported from Africa and South America. Description of the cases has shown the histological hallmark to be the presence of ballooning hepatocytes with fat drops surrounding the nucleus (spongiocytes or morula cells).

METHODS

Experimental reproduction of this syndrome for the verification of a possible role of a specific HDV strain was performed by the inoculation of serum and liver extracts from African patients (Bangui-Central African Republic), who died with this syndrome, into American woodchuck carriers of WHV (WC 231,144), the results of which were then compared with animals inoculated with a reference wild HDV strain (WC 300,173,154), and those which received material from a European fulminant HDV case (WC 88,93).

RESULTS

Following the initial inoculation, the animals receiving African inocula had a delayed anti-HDV seroconversion, high mortality and showed the presence of spongiocytes, while the other animals had a classical evolution of HDV superinfection in woodchucks. Furthermore, the African inocula caused less inhibition of WHV replication, as well as a predominant cytoplasmic expression of HDAg, in contrast to the animals which received the other inocula. The second passage experiments gave similar results.

CONCLUSIONS

We conclude that this peculiar form of HDV fulminant hepatitis can be experimentally reproduced and might be specifically related to a more pathogenic strain.

The French experience of treatment of chronic type D hepatitis with a 12-month course of interferon alpha-2B. Results of a randomized controlled trial

Hepatitis due to hepatitis delta virus (HDV) infection is generally associated with severe histological abnormalities and rapid progression of the disease. To assess the efficacy of recombinant interferon-a2b in treatment of chronic delta hepatitis, 22 patients were entered into a randomized controlled trial: 11 received interferon-a2b subcutaneously three times weekly for 12 months (5 MU/m2 for 4 months and then 3 MU/m2 for a further 8 months) and 11 were untreated. All patients were followed up for 6 months after the completion of therapy. Nine treated patients completed the trial: one was withdrawn with hyperthyroidism and one committed suicide. Serum ALT levels were normalized or significantly reduced, always within 3 months of initiating treatment, and remained so in 73% of treated patients at the 4th month and in 54.5% at the 12th month, compared with 18% and 18%, respectively, in the untreated group. Moreover, in seven of nine treated patients, interferon was associated with the clearance of serum HDV-RNA, associated with amelioration of the histological picture, whereas this occurred in only four of 11 untreated patients. On cessation of therapy, all patients but one experienced a biological and/or virological relapse over the 6-month follow up. In conclusion, our data confirm that HDV is sensitive to inhibition by interferon-a2b, although the schedule used did not achieve permanent control of the disease. The adverse effects of interferon require consideration; in particular, care will be needed to avoid serious psychiatric side effects.

Duck hepatitis B virus infection, aflatoxin B1 and liver cancer in ducks

The association between chronic infection by hepadnaviruses isolated from human (HBV), woodchuck (WHV), ground squirrel (GSHV) and development of hepatocellular carcinoma (HCC) in their respective hosts is well established (reviewed in [11, 15, 17]). By contrast, the association of duck hepatitis B virus (DHBV) infection with HCC is less documented. Pekin ducks congenitally infected with DHBV and followed for several years throughout the world do not develop liver tumors: HCC has been found only in domestic ducks from a single area of China, Qidong. Several factors such as DHBV carrier rate, breed and age of ducks, subtype of DHBV and environmental carcinogens are suspected to contribute to this striking difference between the geographical repartition of liver cancer in DHBV-carrier ducks. In this brief review we will consider successively the role of these different factors in duck liver oncogenesis.

Effects of 2'-fluorinated arabinosyl-pyrimidine nucleosides on duck hepatitis B virus DNA level in serum and liver of chronically infected ducks

The 2'-fluorinated arabinosyl-pyrimidine nucleosides, 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-iodocytosine (FIAC) and 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-methyluracil (FMAU), are new antiviral compounds with in vitro inhibitory activity against the DNA polymerase of hepadnaviruses. Those compounds also induced permanent inhibition of viral replication in woodchucks chronically infected by woodchuck hepatitis virus. The effects of these antiviral compounds were assessed in ducks chronically infected by duck hepatitis B virus (DHBV). Following intraperitoneal administration for 5 days, FMAU (2 mg/kg/day) and FIAC (10 mg/kg/day) induced a transient decrease in DHBV replication, as shown by the decrease in both the serum and liver DHBV DNA level. After stopping therapy, DHBV replication rebounded immediately to the pretreatment level. The supercoiled form of liver viral DNA was found to be less affected by the therapy. By contrast, no obvious antiviral effect was observed with vidarabine monophosphate (ara-AMP) (80 mg/kg/day) therapy. No sign of toxicity was observed during the course of the treatment. These preliminary results confirmed in the DHBV model the higher efficacy of FIAC and FMAU as compared to ara-AMP. Pharmacokinetic studies are needed to explain the differences observed in viral replication in these 2 models of HBV infection.

The isolation and culture of DHBV-infected embryo and duckling hepatocytes and the effect of aflatoxin B1 or irradiation on these cells

The preparation of primary cultures of control and DHBV-infected duck hepatocytes from embryos and young ducklings is described. Cultures of both embryo and duckling hepatocytes secreted duck serum proteins. Cultures of hepatocytes established from ducklings maintained initial morphology for up to 3 weeks in culture and also exhibited high levels of metabolism of aflatoxin B1. Embryonic cell cultures rapidly lost ability to metabolise AFB1 and became overgrown by spindle-shaped cells. Both embryo and duckling cell cultures secreted infective DHBV, and had intracellular replicative forms of the virus. No integration of the virus into the duck genome was observed, and attempts to induce viral integration in the duckling hepatocytes using irradiation and aflatoxin B1 toxicity were unsuccessful. The results of the study lend further support to the suggestion that the rarity of liver cancer in DHBV-infected experimental ducks is related to an innate resistance of the hepatocytes to develop DHBV-DNA integration. Another possibility may be related to the lower oncogenic potential of the DHBV strain used for the study. However DHBV infected duckling hepatocytes would appear to offer a suitable material for studying viral replication and mechanisms of aflatoxin B1 toxicity during prolonged cell culture.

Early and frequent detection of HBxAg and/or anti-HBx in hepatitis B virus infection

To clarify the significance of the X gene of hepatitis B virus, we have tested for anti-HBx in the serum and HBxAg in the liver at different stages of the natural history of hepatitis B virus infection. Sera were screened by enzyme-linked immunosorbent assay and positive results confirmed by immunoblot. Purified recombinant MS2 Pol-HBx fusion protein was used as target for both assays. Among serial sera of patients with nonfulminant acute hepatitis, 24 of 64 patients (37.5%) were positive for anti-HBx. In fulminant cases, 15 of 36 patients (42%) had anti-HBx. In chronic hepatitis patients with high rates of hepatitis B virus replication, we found a significantly (p less than 0.01) higher prevalence of anti-HBx, 14 of 25 patients (56%), than in those with low replication, 14 of 66 patients (21%), or among asymptomatic HBsAg carrier blood donors (20 of 126 = 16%) without detectable hepatitis B virus replication (p less than 0.0001). The highest prevalence of anti-HBx was found in HBsAg carriers with cirrhosis (41 of 54 patients = 76%) and/or with hepatocellular carcinoma (18 of 33 patients = 54%). The findings suggest that anti-HBx appears as a common and early marker of hepatitis B virus infection, transient in self-limited hepatitis but persisting with progression to chronicity. In chronic hepatitis, the prevalence of anti-HBx correlated with the intensity and duration of hepatitis B virus replication but neither with the severity of the liver disease nor with malignant transformation per se.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effects of 2'-fluorinated arabinosyl-pyrimidine nucleosides on woodchuck hepatitis virus replication in chronically infected woodchucks

The treatment of woodchuck hepatitis virus infections with 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-iodocytosine (FIAC) and 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-methyluracil (FMAU), given intraperitoneally, caused complete and permanent decrease of serum virus endogenous DNA polymerase and viral DNA in all treated woodchucks but was associated with severe toxicity. By contrast 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-ethyluracil (FEAU) induced a sustained, although less dramatic, decrease of viral replication without apparent toxic effect. FEAU was also effective when given orally. However, in both cases this inhibitory effect was transient.

Virus-neutralizing monoclonal antibody to a conserved epitope on the duck hepatitis B virus pre-S protein

In this study we used duck hepatitis B virus (DHBV)-infected Pekin ducks and heron hepatitis B virus (HHBV)-infected heron tissue to search for epitopes responsible for virus neutralization on pre-S proteins. Monoclonal antibodies were produced by immunizing mice with purified DHBV particles. Of 10 anti-DHBV specific hybridomas obtained, 1 was selected for this study. This monoclonal antibody recognized in both DHBV-infected livers and viremic sera a major (36-kilodalton) protein and several minor pre-S proteins in all seven virus strains used. In contrast, pre-S proteins of HHBV-infected tissue or viremic sera did not react. Thus, the monoclonal antibody recognizes a highly conserved DHBV pre-S epitope. For mapping of the epitope, polypeptides from different regions of the DHBV pre-S/S gene were expressed in Escherichia coli and used as the substrate for immunoblotting. The epitope was delimited to a sequence of approximately 23 amino acids within the pre-S region, which is highly conserved in four cloned DHBV isolates and coincides with the main antigenic domain as predicted by computer algorithms. In in vitro neutralization assays performed with primary duck hepatocyte cultures, the antibody reduced DHBV infectivity by approximately 75%. These data demonstrate a conserved epitope of the DHBV pre-S protein which is located on the surface of the viral envelope and is recognized by virus-neutralizing antibodies.

Prolonged duck hepatitis B virus replication in duck hepatocytes cocultivated with rat epithelial cells: a useful system for antiviral testing

Duck cultured hepatocytes from Pekin ducks naturally infected by duck hepatitis B virus can remain functional twice longer if a coculture system with rat liver epithelial cells is used instead of ordinary primary culture. The use of a selective medium in which ornithine and lactate replaced arginine and glucose, respectively, allowed viral replication initiated in vivo to be maintained in the coculture for 2 months. Several antiviral compounds including the pyrophosphate analog (phosphonoformic acid) or nucleoside analogs (9 beta-arabinofuranosyl AMP, 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-iodocytosine, 1,2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl-5-ethyluracil and 1,2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl thymine) were studied in both culture systems for their ability to inhibit duck hepatitis B virus replication. Hepatocytes were treated for 7 days with 1,2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl-5-ethyluracil (10 microM) and 1,2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl thymine (0.5 microM) or for 14 days with 9 beta-arabinofuranosyl AMP (90 microM), phosphonoformic acid (100 microM) and 1-(2'-deoxy-2'-fluoro-beta-D-arabinofuranosyl)-5-iodocytosine (6 microM). The effects of the drugs on viral replication were monitored by testing for duck hepatitis B virus DNA in the culture supernatant and in the cells by molecular hybridization.(ABSTRACT TRUNCATED AT 250 WORDS)

Main properties of duck hepatitis B virus DNA polymerase: comparison with the human and woodchuck hepatitis B virus DNA polymerases

The main properties of the duck hepatitis B virus (DHBV) DNA polymerase have been studied and compared with those of the human hepatitis B virus (HBV) and of the woodchuck hepatitis virus (WHV) DNA polymerases. All 3 enzymes are active under high salt conditions in the presence of high magnesium concentration. DHBV DNA polymerase was found less sensitive to ethanol and to operate at higher optimal pH than the HBV and WHV DNA polymerases. Like the other two viral endogenous DNA polymerases, the DHBV enzyme was strongly inhibited by phosphonoformic acid but not by aphidicolin, sulfhydryl group blockers or phosphonoacetic acid. Inhibition of DHBV DNA polymerase by the triphosphate derivatives of several nucleoside analogs appeared similar to that reported for HBV or WHV endogenous polymerase. FIACTP was the most, and ACVTP the least effective inhibitor; BVdUTP was of intermediary potency; araCTP and araTTP had a greater inhibitory effect on DHBV DNA polymerase than HBV or WHV DNA polymerase. The similarities in the properties of DHBV and HBV DNA polymerase justify the use of the duck hepatitis B polymerase model for screening and evaluation of potentially active drugs against HBV infection.

Changes of hepatitis B virus (HBV) markers during prolonged recombinant interferon alpha-2A treatment of chronic HBV infection

Eleven HBsAg chronic carriers were treated with recombinant-interferon (rIFN)-alpha-2A with either 20 X 10(6) (n = 6) or 10 X 10(6) IU/m2 body surface (n = 5), i.m. twice weekly for 6 months. HBV-markers were tested monthly for 15 months. Throughout the follow-up, 6 patients (54%) became HBeAg, HBV-DNAp and HBV-DNA negative (responders). In addition, 8 were HBcAg-negative, 10 anti-HBc-IgM-negative and 2 HBsAg/IgM complexes negative. All patients gave polymerized human serum albumin receptors and HBsAg-positive results. The low rIFN dose seems to be more efficient for clearing HBV-markers than the high dose. Responder patients already showed lower (P less than 0.05) HBsAg concentration and HBsAg/IgM complexes levels in their basal samples as compared to non-responders, and exhibited under rIFN treatment significant decreases (P less than 0.05) in all HBV-markers studied. In conclusion, the most reliable HBV-markers to be assayed in the evaluation of antiviral therapy are HBV-DNA, HBV-DNAp or HBcAg. The testing of pHSA-R, HBsAg/IgM complexes and anti-HBc-IgM does not seem to be very useful.

Therapeutic potential of acyclovir and of the interferons in HBV-related chronic active hepatitis due to HBV with or without HDV superinfection

Acyclovir only demonstrated activity in CAH patients with low HBV replication (DNA-p less than or equal to 80 cpm). In those, oral acyclovir 4 g/day for 4 months was able to permanently inhibit DNA-p in 5/5 cases without significant side-effects.

Therapeutic activity of vidarabine in symptomatic chronic active hepatitis related to HBV

The potential inhibitory effects of nucleoside analogues such as ARA-A and acyclovir on HBV-DNA-polymerase were first demonstrated in vitro and then confirmed in vivo in open dose finding studies. The therapeutic efficacy of both ARA-A and ARA-AMP which appeared the most potent drugs was then confirmed by various studies in symptomatic HBeAg-positive patients. These studies demonstrated a similar benefit of therapy with 38 and 40% of treated patients given ARA-A and ARA-AMP, respectively, who permanently cleared HBV replication after a single course, and 67-80% who did so after two courses. Significant improvement in transaminases and histologic activity was also documented (P less than 0.001). Myalgias were observed in 10 and 30% of the patients, respectively. Patients who failed to respond to nucleosides, and those coinfected with HDV, were treated with interferons. Out of 8 cases of HDV/CAH given 5 MU thrice weekly of fibroblast beta-interferon (UPSA) for 3 months, DNA-p activity fell transiently in all 6 initially elevated cases. A parallel decrease in anti-HD titers (P less than or equal to 0.05), inflammation (P less than or equal to 0.001) and necrosis (P less than or equal to 0.05) were observed. alpha-Recombinant interferon was given i.m. for 4 months (2-7 MU/m2 X 2/7 days) to 10 CAH with high DNA-p values. HBV replication was permanently inhibited in 4 cases and dramatically reduced in 3 additional patients. Three failed to respond. Careful monitoring of DNA-p values appeared to be the single most important factor in assessing activity.