Multiple Effects of Silymarin on the Hepatitis C Virus Lifecycle

Abstract

Silymarin, an extract from milk thistle (Silybum marianum), and its purified flavonolignans have been recently shown to inhibit hepatitis C virus (HCV) infection, both in vitro and in vivo. In the current study, we further characterized silymarin's antiviral actions. Silymarin had antiviral effects against hepatitis C virus cell culture (HCVcc) infection that included inhibition of virus entry, RNA and protein expression, and infectious virus production. Silymarin did not block HCVcc binding to cells but inhibited the entry of several viral pseudoparticles (pp), and fusion of HCVpp with liposomes. Silymarin but not silibinin inhibited genotype 2a NS5B RNA-dependent RNA polymerase (RdRp) activity at concentrations 5 to 10 times higher than required for anti-HCVcc effects. Furthermore, silymarin had inefficient activity on the genotype 1b BK and four 1b RDRPs derived from HCV-infected patients. Moreover, silymarin did not inhibit HCV replication in five independent genotype 1a, 1b, and 2a replicon cell lines that did not produce infectious virus. Silymarin inhibited microsomal triglyceride transfer protein activity, apolipoprotein B secretion, and infectious virion production into culture supernatants. Silymarin also blocked cell-to-cell spread of virus. Conclusion: Although inhibition of in vitro NS5B polymerase activity is demonstrable, the mechanisms of silymarin's antiviral action appear to include blocking of virus entry and transmission, possibly by targeting the host cell.

Identification of hepatoprotective flavonolignans from silymarin

“…Moreover, silymarin displays weak polymerase inhibition against four clinical isolates of genotype 1b HCV RdRps, and silymarin does not inhibit HCV replication in noninfectious replicon cell lines (13). Therefore, we propose that polymerase inhibition by the natural compounds, although demonstrable in vitro, may not contribute to anti-HCVcc action in vitro, and plays a limited role in antiviral effects in patients with chronic hepatitis C when silymarin is taken orally.…”

“…Silymarin inhibits HCV NS5B polymerase activity, albeit at concentrations 5-to 10-fold higher than required for HCVcc inhibition (13). We therefore tested the pure compounds for their ability to inhibit JFH-1 NS5B polymerase activity.…”

“…Indeed, we have shown that silymarin blocks virus entry and fusion, and virus production (13). To determine if silymarin contains antioxidant functions in the context of HCV infection, we treated infected cells with silymarin, then labeled cells with the oxidant reactive dye, H2DCFDA, and measured fluorescence by microscopy.…”

“…Thus, silymarin displays antiviral, anti-inflammatory, and immunomodulatory functions in human liver and immune cells. We (13) and others (14) have recently shown that silymarin can also block in vitro HCV NS5B polymerase activity at high concentration. Therefore, in the current study, we screened the seven major flavonolignans and one flavonoid that comprise silymarin for antiviral, antipolymerase, anti-NF-κB, and immunomodulatory actions.…”

Modulation of PI3K-LXRα-dependent lipogenesis mediated by oxidative/nitrosative stress contributes to inhibition of HCV replication by quercetin

“…[16][17][18] Information on the potential benefits of flavonoids in the treatment of hepatitis C is relatively limited and sometimes contradictory, 19,20 although some flavonoids, including quercetin, one of the most abundant flavonol-type flavonoids present in the human diet, seem to inhibit the replication of HCV. [21][22][23] On the basis of these data, in the current research we explored the effects of different natural antioxidant flavonoids on HCV replication in an in vitro model. We have previously described that important differences exist between flavonoids with different structural features in their capacity to abrogate the generation of different ROS/RNS.…”