Effects of baicalein on Sendai virus in vivo are linked to serum baicalin and its inhibition of hemagglutinin-neuraminidase

Parainfluenza viruses are significant respiratory-tract pathogens that are notorious for infecting children. However, there are no clinical drugs to control the infection caused by these viruses. Sendai virus (SeV) belongs to the family Paramyxoviridae and causes fatal pneumonia in mice, its natural host. Baicalein is a flavonoid derived from the root of Scutellaria baicalensis, which is a traditional Chinese medicine that has been used for hundreds of years and has demonstrated a variety of biological activities. Our findings reveal that oral administration of baicalein to mice infected with Sendai virus results in a significant reduction in virus titers in the lungs and protection from death. The in vivo inhibitory effects of baicalein on Sendai virus are determined by baicalin in the serum. The mean IC50 of baicalin was 0.71 mu g/ml in an HA inhibition assay and 3.22 mu g/ml in an NA inhibition assay. The mean IC50 of baicalin in a CPE assay was measured to be 0.70 mu g/ml, and significant inhibition was observed in a plaque assay at a concentration of 1.6 mu g/ml baicalin in overlay medium, which suggests that baicalein is a potential anti-parainfluenzaviral agent in vivo.