Biliverdin Inhibits Hepatitis C Virus Nonstructural 3/4A Protease Activity

Induction of heme oxygenase-1 (HO-1) inhibits hepatitis C virus (HCV) replication. Of the products of the reaction catalyzed by HO-1, iron has been shown to inhibit HCV ribo-nucleic acid (RNA) polymerase, but little is known about the antiviral activity of biliverdin (BV). Herein, we report that BV inhibits viral replication and viral protein expression in a dose-dependent manner in replicons and cells harboring the infectious J6/JFH construct. Using the SensoLyte 620 HCV Protease Assay with a wide wavelength excitation/emission (591 nm/622 nm) fluorescence energy transfer peptide, we found that both recombinant and endogenous nonstructural 3/4A (NS3/4A) protease from replicon microsomes are potently inhibited by BV. Of the tetrapyrroles tested, BV was the strongest inhibitor of NS3/4A activity, with a median inhibitory concentration (IC 50 ) of 9 l M, similar to that of the commercial inhibitor, AnaSpec (Fremont, CA) #25346 (IC 50 5 l M). Lineweaver-Burk plots indicated mixed competitive and noncompetitive inhibition of the protease by BV. In contrast, the effects of bilirubin (BR) on HCV replication and NS3/4A were much less potent. Because BV is rapidly converted to BR by biliverdin reductase (BVR) intracellu-larly, the effect of BVR knockdown on BV antiviral activity was assessed. After greater than 80% silencing of BVR, inhibition of viral replication by BV was enhanced. BV also increased the antiviral activity of a -interferon in replicons. Conclusion : BV is a potent in-hibitor of HCV NS3/4A protease, which likely contributes to the antiviral activity of HO- These findings suggest that BV or its derivatives may be useful in future drug therapies targeting the NS3/4A protease. (HEPATOLOGY 2010;52:1897-1905)