Biliverdin Inhibits Hepatitis C Virus Nonstructural 3/4A Protease Activity: Mechanism for the Antiviral Effects of Heme Oxygenase?

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 ribonucleic acid (RNA) polymerase, but little is known about the antiviral activity of biliverdin (BV) Herein, we report that BY 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 BY Of the tetrapyrroles tested, BY was the strongest inhibitor of NS3/4A activity, with a median inhibitory concentration (IC50) of 9 mu M, similar to that of the commercial inhibitor, AnaSpec (Fremont, CA) #25346 (IC50 5 mu M) Lineweaver-Burk plots indicated mixed competitive and noncompetitive inhibition of the protease by BY In contrast, the effects of bilirubin (BR) on HCV replication and NS3/4A were much less potent Because BY is rapidly converted to BR by biliverdin reductase (BVR) intracellularly, the effect of BVR knockdown on BY antiviral activity was assessed After greater than 80% silencing of BVR, inhibition of viral replication by BY was enhanced BY also increased the antiviral activity of alpha-interferon in rephcons Conclusion BY is a potent inhibitor of HCV NS3/4A protease, which likely contributes to the antiviral activity of HO-1 These findings suggest that BY or its derivatives may be useful in future drug therapies targeting the NS3/4A protease (HEPATOLOGY 2010,52 1897-1905)