Inhibition of hepatitis B virus in HepG2.2.15 by indirubin through suppression of a polypyrimidine tract-binding protein

Chronic hepatitis B virus (HBV) infection continues to be a public health burden worldwide. With the current treatment strategy, a limited number of patients achieve "functional cure". There is a need for novel therapeutic approaches that enable resolution of HBV. In our study, HepG2.2.15 cell lines were used as an in vitro cellular model to assess the antiviral activity of indirubin. The cytotoxicity of indirubin was detected by 3-(4,5-dimethyl- 2-thiazolyl)-2,5-diphenyl-2-H-tetrazolium bromide. HBsAg and HBeAg in the cell culture were determined by enzyme-linked immunosorbent assay, and HBV DNA secretion was measured by real-time fluorescence quantification PCR. The intracellular HBsAg was detected. To demonstrated the mechanisms underlying the anti-HBV activity of indirubin, western blotting and qRT-PCR were performed to detected the expression levels of a polypyrimidine tract-binding protein (PTB). The role of indirubin from Isatisindigotica extracts presented low cytotoxicity. The results demonstrated indirubin effectively reduced the secretion of HBV antigen (HBsAg and HBeAg), and suppressed HBV DNA secretion. In addition, indirubin significantly reduced intracellular HBsAg. Furthermore, indirubin significantly reduced the protein level of PTB. This study is the first to demonstrate that indirubin possesses anti-viral ability and the mechanism may be through down regulating the polypyrimidine tract-binding protein. It could be used as a potential treatment against HBV infection targeting the host factor.