Animal models for the understanding and control of HBV and HDV infections

Experimental transfection of Macaca sylvanus with cloned human hepatitis B virus

Due to the absence of easily accessible animal models for the study of hepatitis B virus (HBV), the possibility of using Macaca sylvanus, a monkey originating from Morocco, North Africa, was investigated. Three monkeys were intrahepatically inoculated with a replication-competent head-to-tail HBV DNA plasmid dimer construct. The HBV surface antigen and HBV DNA were detected prior to alanine aminotransferase elevation in the serum of two of three HBV-inoculated monkeys at day 2 post-transfection and persisted for several weeks. This indicates that transfected animals developed markers of HBV infection. In addition, electron microscopy of the serum 3 weeks post-transfection showed the presence of virus particles whose shape and size were similar to complete 42 nm HBV Dane particles. Histological examination of liver tissues also revealed pathological changes not observed in uninfected controls, which strongly suggested acute hepatitis. HBV DNA was also detected by PCR in these monkey livers. Taken together, these results indicate that HBV can successfully replicate in this model and that M. sylvanus could be a potentially useful new primate model for the study of HBV replication.

Cell-based and animal models for hepatitis B and C viruses

Reliable cell-based assays and animal models have been developed for evaluating agents against hepatitis B virus. Although much progress has been made, in vitro and in vivo assays for hepatitis C virus are still on the horizon. Advances towards establishing inexpensive and reliable experimental models have accelerated the development of therapeutic modalities for these life-threatening viral infections. The characterization of well-defined viral targets coupled with improved molecular diagnostic technologies have illuminated this field.

Use of a prenylation inhibitor as a novel antiviral agent

No specific therapy exists for hepatitis delta virus (HDV), which can cause severe liver disease. Molecular genetic studies have implicated the prenylation site of large delta antigen as a critical determinant of HDV particle assembly. We have established a cell culture model which produces HDV-like particles, and we show that delta antigen prenylation can be pharmacologically inhibited by the prenylation inhibitor BZA-5B. Furthermore, BZA-5B specifically abolishes particle production in a dose-dependent manner. These results demonstrate that the use of such a prenylation inhibitor-based antiviral therapy may be feasible and identify a novel class of potential antiviral agents.

Woodchuck hepatitis virus-induced carcinoma as a relevant natural model for therapy of human hepatoma

BACKGROUND

Eastern American woodchuck (Marmota monax), naturally infected with woodchuck hepatitis virus, a virus similar to human hepatitis B virus, develops liver cancer with a high prevalence.

AIMS

The aim of this work was to assess Marmota monax as a model of human hepatocellular carcinoma, especially to assess new potential adjuvant therapies after surgical resection.

METHODS

Forty-four woodchuck hepatitis virus-infected animals were regularly screened by ultrasound examination from the age of 18 months and for a 30-month period. One or more liver tumors were diagnosed in 31 animals (70%). Five of them with multifocal tumor or poor general status were considered unsuitable for surgery. The other 26 were operated on. At laparotomy no tumor was found in three.

RESULTS

The 18 liver tumors studied were hepatocellular carcinomas, grossly and microscopically similar to human hepatocellular carcinoma. Peritumoral parenchyma studied in 13 specimens was always non-cirrhotic but adequate staining demonstrated patterns of fibrosis in four cases. Clear evidence of chronic active hepatitis, periportal hepatitis and steatosis were demonstrated in five, seven and one of the 13 specimens, respectively. Tumors were treated by tumorectomy in eight animals, by alcoholization in seven and by laser photocoagulation in one. A simple tumor biopsy was performed in the other seven. Ten animals died postoperatively. All the survivors in the tumorectomy group died from tumor recurrence within 10-18 months after surgery.

CONCLUSIONS

It is concluded that woodchuck hepatitis virus-induced liver carcinoma is a natural model of human hepatocellular carcinoma with similar pathology and natural history, including early ultrasonic detection and tumor recurrence after resection. Tumor excision is feasible in this animal model, which now provides the basis for assessment of new potential adjuvant therapies for human hepatocellular carcinoma in an attempt to reduce the high recurrence rate after surgical resection in humans.

HBV and HDV replication in experimental models: effect of interferon

The use of HBV and HDV experimental models has significantly contributed to understand the viral life cycle and to systematically test antiviral effects of various drugs on a pre-clinical level. Similar replication strategies of related hepadna viruses permit the use of chimpanzees (Pan troglodytes), woodchucks (Marmota monax), ground and tree squirrels (Spermophilus beecheyi) or Pekin ducks (Anas domesticus) as appropriate animal models. Cell culture systems for in vitro infection or transfection using both primary cultures of human and non-human hepatocytes and non-hepatocytes and cell lines have recently been identified. The advantages and restrictions of these experimental models with respect to evaluation of interferon effects on viral and hepatocellular gene expression are discussed.