Our study provides, for the first time, clear evidence that the extract of H. perforatum, containing hyperoside, quercitrin, quercetin, pseudohypericin, and hypericin, possess anti-IBV activities. Furthermore, its anti-IBV effect may be associated with reduced mRNA expression levels of the pro-inflammatory cytokines IL-6, TNF-α by NF-κB signaling pathway, and related to up-regulate mRNA expression levels of type I interferon through the MDA5 signaling pathway, and could be useful for the development of new antiviral agents. However, further studies are required to elucidate its detail mechanism of action.
The minimum effective dose of HPE in these studies was 31.25 mg/kg/day, which was administered twice daily for 5 d beginning 4 h prior to virus exposure. Below a dosage of 2000 mg/kg/day, almost all treated mice survived, which suggests that HPE is of low toxicity. Ribavirin’s minimum effective dose was 40 mg/kg/day with the LD50 determined to be 200 mg/kg/day. Delay of the initiation of either HPE or ribavirin therapy, using approximately 1/3 LD50 dose each time, could still be protective as late as 48 h after exposure to the IAV. While both agents appeared to have similar efficacy against IAV infections, HPE was considered to be less toxic and may warrant further evaluation as a possible therapy for influenza.