Anti-influenza A virus mechanism of three representative compounds from Flos Trollii via TLRs signaling pathways

Abstract Ethnopharmacological relevance Flos Trollii is the dried flowers of Trollius chinensis. It has been used as a traditional herbal medicine for the treatment of upper respiratory tract infection, tonsillitis and pharyngitis in China for a long history. Veratric acid, vitexin, and trolline are the representative compounds of phenolic acids, flavonoids and alkaloids in this herbal medicine. All of these three compounds show antiviral activity which is related to the efficacy of Flos Trollii. Aim of the study To investigate the anti-influenza A virus mechanism of the three representative compounds from the perspective of regulating TLRs signaling pathways, so as to understand the relevant efficacy of Flos Trollii. Materials and methods Influenza A virus A/FM/1/47 (H1N1) and mouse peritoneal macrophages (RAW264.7) were used in the whole process of investigation. MTT assay was conducted to select the appropriate experimental concentrations of the three compounds on RAW264.7 cells. Western blot, RT-PCR, and ELISA assays were performed to determine the protein and mRNA expression of key factors and related inflammatory factors of TLRs signaling pathways. Griess method was employed to detect the production of NO. Results The three representative compounds reduced the inflammatory factors including NO, IL-6, and TNF-α and enhanced the production of IFN-β through dynamically regulating the TLRs 3, 4 and 7 pathways. Veratric acid significantly down-regulated the protein expression of TLR3 and IRF3 as well as the mRNA expression of TBK1 and TRIF. Vitexin significantly down-regulated the protein expression of TBK1 and IRF3 as well as the mRNA expression of TLR3, TBK1, TRIF and IRF3 while up-regulated the protein expression of TLR4 and IKKα. Trolline significantly down-regulated the protein expression of TLR7 whereas significantly up-regulated the protein expression of TLR4, IKKα and TAK1. Conclusions The three representative compounds from Flos Trollii play their parts in anti-H1N1 viral effect through partially down-regulating TLRs 3 and 7 pathways and up-regulating TLR4 pathway. They counteract the inflammatory injury caused by excessive production of NO, IL-1, IL-6, and TNF-α induced by virus infection and enhance the production of IFN-β so as to eliminate the virus.