34 With respect to CO effects on HCV replication (Fig. 3A, B), we only found transient reduction of replication, which was detectable at 6 hours after the onset of experiments but

was no longer detectable after 24 hours. The mechanism selleck chemical of CO-induced transient repression of HCV replication remains elusive and might be partially attributable to a slight induction of HO-1 expression. Biliverdin has been shown to reduce replication of HIV35 and human herpes virus type 6,36 whereas it did not interfere with replication of human herpesvirus type 1 or cytomegalovirus.36 It has been speculated that biliverdin might interfere with cellular processes specific for replication of certain viruses,36 and, in case of HIV, also directly inactivate viral particles.35 Conversely, oxidative stress seems to trigger viral replication,29 a process that might be a target of the antioxidant biliverdin. In fact, it has been shown that HCV induces oxidative buy Palbociclib stress27, 28 and that oxidative stress interferes with antiviral gene expression.30 We also found that moderate oxidative stress in replicon cells triggered HCV replication (Fig. 5A). Biliverdin incubation induced expression of antiviral alpha interferons, for example, interferon alpha2 and alpha17 (Fig. 5B). Downstream effects of interferon alpha treatment, such

as expression of PKR or OAS, were also enhanced by biliverdin (Fig. 5C), underlining its antiviral effect. It has been shown that phosphorylation of translation initiation factor eIF2alpha by interferon-inducible protein kinase PKR is able to suppress HCV replication in JFH1-infected Huh-7 cells, further elucidating the mechanism of IFN alpha–induced inhibition of HCV replication.37 Likewise, under conditions of heme deficiency, heat shock, or oxidative stress, heme-regulated eIF2alpha kinase is able to phosphorylate eIF2alpha and inhibit translation.38 In fact, expression of both kinases was found to be increased after biliverdin incubation (Fig. 5C). These findings do not exclude an additional and yet unknown effect of biliverdin on HCV replication that is independent of reduction in oxidative stress.

Recently, it has been shown that oxidative stress also might interfere with HCV replication,39 as we selleck observed for higher H2O2 concentrations (Fig. 5A). This effect has been attributed to modulation of the MEK-ERK1/2 signaling pathway,40 and also might be a result of reduced cellular viability and proliferation, because oxidative stress is involved in regulation of both hepatocyte apoptosis and proliferation.40 In fact, modulation of oxidative stress has been proposed as a therapy concept for HCV. A clinical trial showed that patients might benefit from a combination treatment with IFNalpha and the anti-oxidant N-acetyl-cystein in comparison with IFN alpha treatment alone,41 although others did not observe this effect.