The role of interferon in the treatment of viral hepatitis

HCV-hepatocellular carcinoma: new findings and hope for effective treatment

We present here a comprehensive review of the current literature plus our own findings about in vivo and in vitro analysis of hepatitis C virus (HCV) infection, viral pathogenesis, mechanisms of interferon action, interferon resistance, and development of new therapeutics. Chronic HCV infection is a major risk factor for the development of human hepatocellular carcinoma. Standard therapy for chronic HCV infection is the combination of interferon alpha and ribavirin. A significant number of chronic HCV patients who cannot get rid of the virus infection by interferon therapy experience long-term inflammation of the liver and scarring of liver tissue. Patients who develop cirrhosis usually have increased risk of developing liver cancer. The molecular details of why some patients do not respond to standard interferon therapy are not known. Availability of HCV cell culture model has increased our understanding on the antiviral action of interferon alpha and mechanisms of interferon resistance. Interferons alpha, beta, and gamma each inhibit replication of HCV, and the antiviral action of interferon is targeted to the highly conserved 5'UTR used by the virus to translate protein by internal ribosome entry site mechanism. Studies from different laboratories including ours suggest that HCV replication in selected clones of cells can escape interferon action. Both viral and host factors appear to be involved in the mechanisms of interferon resistance against HCV. Since interferon therapy is not effective in all chronic hepatitis C patients, alternative therapeutic strategies are needed to treat chronic hepatitis C patients not responding to interferon therapy. We also reviewed the recent development of new alternative therapeutic strategies for chronic hepatitis C, which may be available in clinical use within the next decade. There is hope that these new agents along with interferon will prevent the occurrence of hepatocellular carcinoma due to chronic persistent hepatitis C virus infection. This review is not inclusive of all important scientific publications due to space limitation.

Interferons alpha, beta, gamma each inhibit hepatitis C virus replication at the level of internal ribosome entry site-mediated translation

Interferon (IFN)-alpha is the standard therapy for the treatment of chronic hepatitis C, but the mechanisms underlying its antiviral action are not well understood. In this report, we demonstrated that IFN-alpha, -beta and -gamma inhibit replication of the hepatitis C virus (HCV) in a cell culture model at concentrations between 10 and 100 IU/ml. We demonstrated that the antiviral actions each of each these IFNs are targeted to the highly conserved 5' untranslated region of the HCV genome, and that they directly inhibit translation from a chimeric clone between full-length HCV genome and green fluorescent protein (GFP). This effect is not limited to HCV internal ribosome entry site (IRES), since these IFNs also inhibit translation of the encephalomyocardititis virus (EMCV) chimeric mRNA in which GFP is expressed by IRES-dependent mechanisms (pCITE-GFP). These IFNs had minimal effects on the expression of mRNAs from clones in which translation is not IRES dependent. We conclude that IFN-alpha, -beta and -gamma inhibit replication of sub-genomic HCV RNA in a cell culture model by directly inhibiting two internal translation initiation sites of HCV- and EMCV-IRES sequences present in the dicistronic HCV sub-genomic RNA. Results of this in vitro study suggest that selective inhibition of IRES-mediated translation of viral polyprotein is a general mechanism by which IFNs inhibits HCV replication.

Purification of an atypical bovine interferon induced in response to heat shock in bovine cultured cells. Characterization in comparison with the classical alpha, beta and gamma interferon

Heat-shock induced factor (HSIF) was excreted by bovine MDBK cells during their recovery period after a heat shock. This factor has the capacity to induce 2',5' oligoadenylate synthetase activity, an enzyme generally by interferon treatment (J Biol Chem (1987) 262, 4806-4811). We have observed that an antiviral state was also produced in response to heat shock. HSIF was purified 10,000-fold and different techniques showed a copurification of both activities. Certain properties of HSIF were established, such as its molecular mass (45 kDa) and isoelectric point (6.8). This cytokine was acid-sensitive as IFN gamma (type II) and temperature labile contrarily to alpha, beta and gamma bovine IFN. Immunoprecipitation and comparative chromatography on lectines or polynucleotides established that HSIF was structurally different from the three classes of bovine IFN. Moreover, two-dimensional electrophoresis and comparative analysis of [35S] methionine-labeled proteins induced by HSIF alpha, beta or gamma bovine IFN showed that HSIF induces a specific set of proteins. Taken together, all these results strongly suggest that HSIF is a new atypical bovine interferon induced in response to heat shock.

Hepatitis B

Hepatitis B remains a major public health problem around the world. The discovery of the hepatitis C virus has diverted interest from hepatitis B to this new virus and the epidemic associated with it, but hepatitis B remains a significant pathogen for millions of people worldwide. The World Health Organization has suggested that universal vaccination of children against hepatitis B should be implemented in an attempt to reduce the enormous morbidity and mortality associated with infection of this virus group. The review seeks to identify all the newer discoveries relating to hepatitis B that have been made in the past decade. Reference is made to the appearance of hepatitis B mutants which are able to infect patients previously infected with the wild strain of the virus. The implications of mutants on vaccination programmes is raised, as are issues relating to treatment of hepatitis B infection.