Effect of ribavirin on the hepatitis C virus (JFH-1) and its correlation with interferon sensitivity.

BACKGROUND The consensus therapy for chronic hepatitis C infection is based on a synergistic combination of pegylated interferon and ribavirin. The therapy leads to a sustained virological response in around 60% of infected patients. The mechanism by which this synergy occurs has not yet been elucidated. Several mechanisms of action have been proposed; one suggests that ribavirin, which is a nucleoside analogue, is incorporated into the RNA strand and generates an increase in the error rate. Such an accumulation of mutations would threaten the integrity of the virus's genetic information. METHODS The effects of ribavirin on the new infectious hepatitis C virus cell culture (HCVcc) system were investigated using Huh-7 cells. Cells were cultured for 1 month in either 0 microM, 20 microM or 50 microM ribavirin. The HCV interferon sensitivity and the NS5A quasispecies were analysed. RESULTS An increase in the mutation rate in the HCV NS5A gene was observed when the infected cells were treated with 50 microM ribavirin for 1 month. Amino acid sequence analysis revealed that ribavirin exerts an increase in G to A transition events as predicted by its mutagenic effect and a selective pressure on the HCV NS5A sequence. Furthermore, ribavirin treatment modified the efficacy of interferon (IFN) treatment. The IFN half-inhibition concentration (IC50) was significantly lower for viruses obtained after 1 month's exposure to 50 microM ribavirin than for viruses cultured in the absence of ribavirin. CONCLUSIONS Ribavirin's mutagenic effect could explain in part its synergistic action with interferon.