Mutagenic effect of ribavirin on hepatitis C nonstructural 5B quasispecies in vitro and during antiviral therapy

Background & Aims: Addition of ribavirin to interferon alfa treatment has substantially increased sustained virologic response rates in patients with chronic hepatitis C (CHC). Ribavirin acts as an RNA virus mutagen in vitro, thereby leading to error catastrophe. However, data in CHC are controversial. Methods: The nonstructural (NS) 5B quasispecies heterogeneity was analyzed in Huh7 cells harboring a subgenomic hepatitis C virus (HCV) replicon system treated with ribavirin or levovirin. Accordingly, NS5B quasispecies were studied in 14 patients with CHC who received ribavirin alone or combined with pegylated interferon alfa both at baseline and during the first weeks of therapy. Analysis of NS3 quasispecies served as control. Results: Cultivation of HCV replicon cells with ribavirin led to higher NS5B mutational frequencies compared with levovirin-treated or untreated cells (P < .05). Patients receiving ribavirin monotherapy showed higher overall mutational frequencies within NS3 and NS5B during therapy as compared with baseline (P < .01). Proportions of ribavirin-specific G-to-A and C-to-T transitions increased (P < .01). Paired analysis confirmed significant mean increases of mutational frequencies of similar to 5%. Ribavirin serum concentrations were positively correlated with mutational frequency changes (P < .05). In patients receiving combination therapy, a decrease of NS5B mutational frequencies (similar to 10%) and lower proportions of G-to-A and T-to-C mutations (P < .01) were detectable. Conclusions: Ribavirin, but not its L-enantiomer levovirin, is a mutagen in HCV replicon cells. In patients with CHC, ribavirin monotherapy exhibits a moderate mutagenic effect early during therapy that is not detectable in combination with pegylated interferon alfa.