In chronic hepatitis C therapy, ribavirin improves the SVR rates in both IFN-containing and all-oral, IFN-free regimens. Although multiple mechanisms of action have been suggested for ribavirin, the main antiviral mechanism in hepatitis C has not yet been

clearly elucidated. Objective: To understand the molecular mechanism of ribavirin antiviral action in hepatitis C virus infection. Methods and Results: Gene expression analysis of uninfected hepatoma (Huh7) cells treated with ribavirin (100 μg/mL) for 24 hours showed that the expression of genes implicated in IFN responses, Fulvestrant in vivo including TLR7, IRF7, IRF9, GBP1 and IFIT2, was induced see more by ribavirin administration. Using the subgenomic genotype 1 b replicon Con-1 in Huh7.5 cells, ribavirin exerted dose-dependent antiviral activity against HCV, reducing the amount of intracellular HCV RNA and the level of NS5A protein after 24 and 48 hours of exposure.

To investigate how ribavirin affects gene transcription in the context of viral infection, we first investigated whether the promoter of IRF7 was modulated by ribavirin. Hepatoma cells expressing the subgenomic genotype 1 b replicon Con-1 and one or both functional interferon-sensitive response elements (ISRE/IRF-E) from different reporter plasmids were treated with different doses of ribavirin, alone or in combination with IFN. Ribavirin activated the IRF7 promoter via IRF-E in a dose-dependent manner. In contrast to IFN, ribavirin had no effect on ISRE, regardless of the ribavirin dose. In addition, IRF7 dominant negative-mediated inhibition of IRF7 resulted in a significant reduction of HCV replication

inhibition. Although IRF7 may be of particular importance because of its role in amplifying the IFN selleck compound signaling cascade, IFN production is initiated by the recognition of TLR, one of the two best-known pattern-recognition receptors. Ribavirin had an effect on TLR7 mRNA expression and, using cells expressing human TLR and an inducible reporter gene, ribavirin selectively activated TLR7 in a dose-dependent manner. In addition, co-incubation of imiquimod or loxoribin (potent activators of TLR7) with ribavirin significantly increased activity of both compounds on TLR7 expressing HEK cells. TLR7 stimulation by ribavirin induced cytokine secretion, hepatoma cells. Conclusion: Ribavirin is a selective TLR7 agonist that increases cytokine secretion by promoting the activation of IRF7, a key factor because of its direct antiviral effect and its role in amplifying the IFN signaling cascade.