In vitro inhibition of influenza virus infection by a crude extract from Isatis indigotica root resulting in the prevention of viral attachment

Mol Med Rep. 2012 Mar;5(3):793-9. doi: 10.3892/mmr.2011.709. Epub 2011 Dec 13.


Isatis indigotica root (IIR) has been widely used as a Chinese medicinal herb to treat regular seasonal influenza over the long history of traditional Chinese medicinal practice. However, its inhibitory activities against influenza virus infections along with the associated mechanisms have not been investigated comprehensively. In this study, the chemical nature, mode of action and in vitro anti-influenza activities of a crude extract (G2) of IIR were characterized. The extract was found to inhibit different subtypes of human or avian influenza viruses at various magnitudes of activity (IC50 0.39‑4.3 mg/ml) in vitro, including A/PR/8/34 (H1N1), A/FM/1/47 (H1N1), A/Aichi/2/68 (H3N2), seasonal influenza (A/Guangzhou/GIRD/02/09 H1N1, B/Guangzhou/GIRD/08/09), novel swine-originating influenza (A/Guangzhou/GIRD/07/09, H1N1), A/Duck/Guangdong/09 (H6N2), A/Duck/Guangdong/94 (H7N3) and A/Chicken/Guangdong/96 (H9N2), while G2 was inactive against respiratory syncytial virus (RSV), adenovirus 3 (ADV3), parainfluenza virus 3 (PIV3) and enterovirus 71 (EV71). An apparent virus titer reduction was detected when the influenza viruses were pretreated with G2, and it was also shown that G2 exhibited inhibitory effects on influenza virus hemagglutination. In addition, G2 played a role in the early stages of infection, which did not easily result in the emergence of virus drug resistance. Thus, G2 may affect the attachment of influenza virus by interfering with the viral particles, thereby preventing the binding of influenza virus to the host cell surface.

Keywords: influenza virus; Isatis indigotica root; crude extract; in vitro.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cell Line
  • Dogs
  • Drugs, Chinese Herbal
  • Hemagglutination Inhibition Tests
  • Host-Pathogen Interactions / drug effects*
  • Influenza A Virus, H1N1 Subtype / drug effects
  • Influenza A Virus, H3N2 Subtype / drug effects
  • Influenza A Virus, H9N2 Subtype / drug effects
  • Influenzavirus A / drug effects*
  • Isatis / chemistry*
  • Plant Extracts / pharmacology*
  • Plant Extracts / toxicity
  • Plant Roots / chemistry
  • Respiratory Syncytial Viruses / drug effects
  • Virus Internalization / drug effects*


  • Drugs, Chinese Herbal
  • Plant Extracts