Antiviral activity of baicalin against influenza A (H1N1/H3N2) virus in cell culture and in mice and its inhibition of neuraminidase

Scutellaria baicalensis Georgi, a Chinese herbal decoction, has been used for the treatment of the common cold, fever and influenza virus infections. In previous studies, we found that oral administration of baicalein resulted in the inhibition of influenza A virus replication in vivo, which was linked to baicalin in serum. However, the effective dose and underlying mechanisms of the efficacy of baicalin against influenza A virus have not been fully elucidated. In this study, the antiviral effects of baicalin in influenza-virus-infected MDCK cells and mice were examined. The neuraminidase inhibition assay was performed to investigate the mechanism of action of baicalin. In vitro results showed that baicalin exhibited a half-maximal effective concentration (EC50) of 43.3 μg/ml against the influenza A/FM1/1/47 (H1N1) virus and 104.9 μg/ml against the influenza A/Beijing/32/92 (H3N2) virus. When added to MDCK cell cultures after inoculation with influenza virus, baicalin demonstrated obvious antiviral activity that increased in a dose-dependent manner, indicating that baicalin affected virus budding. Baicalin had clear inhibitory effects against neuraminidases, with half-maximal inhibitory concentration (IC50) of 52.3 μg/ml against the influenza A/FM1/1/47 (H1N1) virus and 85.8 μg/ml against the influenza A/Beijing/32/92 (H3N2) virus. In vivo studies showed that an intravenous injection of baicalin effectively reduced the death rate, prolonged the mean day to death (MDD) and improved the lung parameters of mice infected with influenza A virus. These results demonstrate that baicalin acts as a neuraminidase inhibitor, with clear inhibitory activities that are effective against different strains of influenza A virus in both cell culture and a mouse model, and that baicalin has potential utility in the management of influenza virus infections.