Pterodontic Acid Isolated from Laggera pterodonta Inhibits Viral Replication and Inflammation Induced by Influenza A Virus

Laggera pterodonta (DC.) Benth. is a traditional Chinese medicine. The previous study revealed that the crude extracts of this herb could inhibit influenza virus infection, but its anti-influenza components and underlying mechanism of action remain unknown. Column chromatography was performed to isolate components from the plant. Activity against influenza virus of the compound was determined by CPE inhibition assay. Neuraminidase (NA) inhibition was measured by chemiluminescence assay. The anti-virus and anti-inflammation effects were determined using dual-luciferase reporter assay, immunofluorescence, quantitative real-time PCR and luminex assay. Pterodontic acid was isolated from L. pterodonta, which showed selective anti-viral activities to H1 subtype of human influenza A virus. Meanwhile, the NA activity was not obviously inhibited by the compound. Further experiments exhibited that the compound can suppress the activation of NF-kappa B signal pathway and export of viral RNP complexes from the nucleus. In addition, it can significantly attenuate expression of the pro-inflammatory molecules IL-6, MIP-1 beta, MCP-1, and IP-10 induced by human influenza A virus (H1N1) and similarly downregulate expression of cytokines and chemokines induced by avian influenza A virus (H9N2). This study showed that in vitro antiviral activity of pterodontic acid is most probably associated with inhibiting the replication of influenza A virus by blocking nuclear export of viral RNP complexes, and attenuating the inflammatory response by inhibiting activation of the NF-kappa B pathway. Pterodontic acid might be a potential antiviral agent against influenza A virus.