Silibinin and related compounds are direct inhibitors of hepatitis C virus RNA-dependent RNA polymerase.
OBJECTIVE
Silymarin is a mixture of flavonolignans extracted from the milk thistle. Silymarin contains several molecules, including silibinin A, silibinin B, isosilibinin A, isosilibinin B, silicristin, and silidianin. Intravenous infusion of silibinin induces dose-dependent reduction of hepatitis C virus (HCV) RNA levels. The aim of this study was to test the principal isomers contained in silymarin preparations for their ability to inhibit HCV enzymatic functions and replication in different models.


METHODS
The inhibitory activity of silymarin components was tested in HCV RNA-dependent RNA polymerase and NS3/4A protease enzyme assays. Their ability to inhibit replication of an HCV genotype 1b replicon model and the JFH1 infectious HCV model in cell culture was also studied.


RESULTS
Silibinin A, silibinin B, their water-soluble dihydrogen succinate forms and Legalon SIL, a commercially available intravenous preparation of silibinin, inhibited HCV RNA-dependent RNA polymerase function, with inhibitory concentrations 50% of the order of 75-100 microM. Silibinin A and silibinin B also inhibited HCV genotype 1b replicon replication and HCV genotype 2a strain JFH1 replication in cell culture. None of these compounds inhibited HCV protease function.


CONCLUSIONS
Silibinin A and silibinin B, as well as Legalon SIL, inhibit HCV replicon and JFH1 replication in cell culture. This effect is at least partly explained by the ability of these compounds to inhibit HCV RNA-dependent RNA polymerase activity. Our results provide a basis for the optimization and subsequent development of members of the Flavonoid family as specific HCV antivirals.
Ahmed-Belkacem
Abdelhakim
A
Research Team Pathophysiology and Therapy of Chronic Viral Hepatitis, INSERM U955, Créteil, France.
Ahnou
Nazim
N
Barbotte
Laetitia
L
Wychowski
Czeslaw
C
Pallier
Coralie
C
Brillet
Rozenn
R
Pohl
Ralf-Torsten
RT
Pawlotsky
Jean-Michel
JM
D000998:Antiviral Agents / Q000494:pharmacology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D024882:Drug Resistance, Viral; D005838:Genotype; D016174:Hepacivirus / Q000187:drug effects* / Q000201:enzymology / Q000235:genetics / Q000254:growth & development; D006801:Humans; D009154:Mutation; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology*; D012324:RNA-Dependent RNA Polymerase / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D000077385:Silybin; D012838:Silymarin / Q000494:pharmacology; D017361:Viral Nonstructural Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D014779:Virus Replication / Q000187:drug effects*; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases
D000998:Antiviral Agents; D019384:Nucleic Acid Synthesis Inhibitors; D012324:RNA-Dependent RNA Polymerase; D011994:Recombinant Proteins; D000077385:Silybin; D012838:Silymarin; D017361:Viral Nonstructural Proteins; C084422:NS3 protein, hepatitis C virus; D012697:Serine Endopeptidases; D043583:Nucleoside-Triphosphatase; D053487:DEAD-box RNA Helicases; D000085242:Viral Proteases; C087036:NS-5 protein, hepatitis C virus