Antiviral Activity of Baicalin Against Infectious Bronchitis Virus

Abstract

Background Baicalin, the main metabolic component of Scutellaria Baicalin Georgi, displays potent anti-inflammatory, anti-oxidant, anti-apoptotic, anti-bactericidal, and antiviral properties. Baicalin was found to be effective in the treatment of infectious bronchitis (IB) in chickens. However, the molecular mechanism of treatment remained unclear. Therefore, in this study, the antiviral activities of baicalin on infectious bronchitis virus (IBV) were evaluated in vitro and in vivo for the first time, to explore the molecular mechanism of baicalin inhibiting IBV replication. Results Treatment with 20 µg/mL baicalin significantly reduced relative mRNA expression and IBV viral titers, a finding confirmed by immunofluorescence studies in chicken embryo kidney (CEK) cells. Baicalin treatment at a dose of 45 mg/kg significantly reduced IBV induced injury in the trachea, lung and kidney. Baicalin treatment also led to an upregulation of both interferon-α (IFN-α) and Interferon-β (IFN-β), with IFN-β increased the most. Although treatment with baicalin did not influence the mRNA expression of melanoma differentiation associated gene 5 (MDA5), Toll-like receptor 3 (TLR3), and Toll-like receptor 9 (TLR9), mRNA levels of mitochondrial antiviral signaling gene (MAVS), TANK binding kinase 1 (TBK1), and Interferon regulatory factor 7 (IRF7) increased, with MAVS showing the largest increase amongst all cytokines measured in vitro. Overexpression of MAVS significantly upregulated the expression of IFN-β and reduced the viral titer of IBV. Knockdown of MAVS significantly affected the antiviral effect of baicalin on IBV. Conclusions Baicalin possesses significant anti-IBV effects in vitro and in vivo. Baicalin-induced increases in the expression of type I interferons in CEK cells after IBV infection is likely linked to increased signaling through the enhanced MAVS expression in the MDA5 pathway. Baicalin’s inhibition of IBV replication was also closely related to MAVS cytokines, but not dependent on MAVS expression. These findings are important to accelerate our understanding of the antiviral effects of baicalin and provide new insights into the development of effective therapeutic strategies.