Anti-diabetic drugs, insulin and metformin, have no direct interaction with hepatitis C virus infection or anti-viral interferon response

Hepatitis C virus (HCV) infection is associated with insulin resistance (IR) and type 2 diabetes (T2D). Chronic HCV patients with IR and T2D appear to have a decreased response to the standard pegylated-interferon-alpha and ribavirin (PEG-IFN/RBV) anti-viral therapy. Insulin and metformin are anti-diabetic drugs regularly used in the clinic. A previous in vitro study has shown a negative effect of insulin on interferon signaling. In the clinic, adding metformin to PEG-IFN/RBV therapy was reported to increase the response rate in chronic HCV patients and it has been suggested this effect derives from an improved anti-viral action of interferon. The goal of this study was to further investigate the molecular insight of insulin and metformin interaction with HCV infection and the anti-viral action of interferon. We used two cell culture models of HCV infection. One is a subgenomic model that assays viral replication through luciferase reporter gene expression. The other one is a full-length infectious model derived from the JFH1 genotype 2a isolate. We found that both insulin and metformin do not affect HCV infection. Insulin and metformin also do not influence the anti-viral potency of interferon. In addition, there is no direct interaction between these two drugs and interferon signaling. Our results do not confirm the previous laboratory observation that insulin interferes with interferon signaling and suggest that classical nutritional signaling through mTOR may be not involved in HCV replication. If metformin indeed can increase the response rate to interferon therapy in patients, our data indicate that this could be mediated via an indirect mechanisms.