2--carbodeoxyguanosine and Hepadnaviridae-Infections

Duck hepatitis B virus (DHBV) DNA synthesis in congenitally infected ducks is inhibited by 2'-deoxycarbocyclic guanosine (2'-CDG). Three months of therapy reduces the number of infected hepatocytes at least 10-fold (W.S. Mason, J. Cullen, J. Saputelli, T.-T. Wu, C. Liu, W.T. London, E. Lustbader, P. Schaffer, A.P. O'Connell, I. Fourel, C.E. Aldrich, and A.R. Jilbert, Hepatology 19:393-411, 1994). The present study was performed to determine the kinetics of disappearance of infected hepatocytes and to evaluate the role of hepatocyte turnover in this process. Essentially all hepatocytes were infected before drug therapy. Oral treatment with 2'-CDG resulted in a prompt reduction in the number of infected hepatocytes. After 2 weeks, only 30 to 50% appeared to still be infected, and less than 10% were detectably infected after 5 weeks of therapy. To assess the possible role of hepatocyte turnover in these changes, 5-bromo-2'-deoxyuridine (BUdR) was administered 8 h before liver biopsy to label host DNA in hepatocytes passing through S phase, and stained nuclei were detected in tissue sections by using an antibody reactive to BUdR. The extent of nuclear labeling after 5 weeks was the same as that before therapy (ca. 1%). However, biopsies taken after 2 weeks of therapy showed a ca. 10-fold elevation in the number of nuclei labeled with BUdR. This result suggested that a rapid clearance of infected hepatocytes by 2'-CDG was caused not just by the inhibition of viral replication but also by an acceleration of the rate of hepatocyte turnover. To test this possibility further, antiviral therapy was carried out with another strong inhibitor of DHBV DNA synthesis, 5-fluoro-2',3'-dideoxy-3'-thiacytidine (524W), which did not accelerate hepatocyte turnover in ducks. 524W administration led to a strong inhibition of virus production but to a slower rate of decline in the number of infected hepatocytes, so that ca. 50% (and perhaps more) were still infected after 3 months of therapy. In addition, histopathologic evaluation of 2'-CDG-treated ducks revealed liver injury, especially at the start of therapy. No liver damage was observed during 524W therapy. These results imply that clearance of infected hepatocytes from the liver is correlated with hepatocyte turnover. Thus, in the absence of immune clearance or other sources for the accelerated elimination of infected hepatocytes, inhibitors of virus replication would have to be administered for a long period to substantial

Topics: Animals; Antigens, Viral; Antiviral Agents; Biopsy; Bromodeoxyuridine; Deoxyguanosine; DNA Replication; DNA, Viral; Ducks; Emtricitabine; Hepadnaviridae Infections; Hepatitis B Virus, Duck; Kinetics; Liver; Time Factors; Virus Replication; Zalcitabine

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.

Topics: Animals; Antiviral Agents; Blotting, Southern; Cells, Cultured; Chronic Disease; Deoxyguanosine; Disease Models, Animal; DNA Replication; DNA, Viral; Dose-Response Relationship, Drug; Ducks; Hepadnaviridae Infections; Hepatitis B Virus, Duck; Liver; Viremia; Virus Replication