Baicalin Is A Naturally Occurring Flavone That Efficiently Inhibits RSV Replication

Respiratory syncytial virus (RSV) is the leading cause of acute respiratory tract viral infection in infants, causing bronchiolitis and pneumonia. Morris discovered this virus and reported it since the 1950s. There are no RSV vaccines available to prevent childhood infection and no effective therapeutic strategy against RSV infection. These factors create an urgent need to find novel compounds and understand the mechanisms of RSV disease.Traditional Chinese medicine Scutellaria baicalensis has a significant effect on respiratory infection, and it has been used in clinical application. S. baicalensis is a species of flowering plant belongs to the Lamiaceae family and its major active component is baicalin. Baicalin possesses multiple biological activities including antibacterial, anti-virus, anti-tumor, anti-inflammatory functions.We evaluated antiviral activities of baicalin against RSV in vitro and in vivo and elaborated the potential mechanism. We first found that baicalin inhibit the RSV replication effectively. The IC50 was estimated at 20μM. Baicalin affect multiple stages of RSV replication. Similarly, we found that the extract of S. baicalensis has antiviral effect against RSV infection. Baicalin is the major ingredient in S. baicalensis extract while the antiviral effect of the other three components is not obvious including baicalein, wogonin and wogenside. Therefore, we speculated that baicalin is the main antiviral active ingredient in S.baicalensis.Further, we evaluated the antiviral activity of baicalin on RSV infected mice model. It is demonstrated that baicalin can effectively ease the lung injury caused by RSV infection and reduce the virus titer in lung tissue of mice. Moreover, baicalin can inhibit the inflammation caused by viral infection, reduce the oxidative damage and invasion of inflammatory cells in the lung tissue, and remit symptoms associated with the virus infection.In conclusion, baicalin is the major ingredient of S.baicalensis and suppresses RSV infection effectively. Baicalin can inhibit the RSV replication and inflammation in mouse model of human RSV disease. Baicalin also alleviates lung injury caused by RSV infection.