Antiviral Activities Of Ethanol Extracts From Folium Syringae Leaves Against Swine Influenza Virus

Swine influenza (SI) is an acute respiratory disease caused by swine influenza virus (SIV)which belongs to the family of the Orthomyxoviridae. It often shows high fever, dullness, loss ofappetite, labored abdominal breathing and coughing. Once occurs, it may cause great economiclost to swine industry, especially, co-infecting with other respiratory disease, such as PRRS. SIVcan not only infects Pig, but although fowl and other mammal such as the human being and horse.And pig can be infected by avian influenza virus (AIV) and human influenza virus, it’s the mixingmill for recombination and reassortment of influenza virus genes and the couveuse for the formingof new popular influenza virus. The feature of SIV and pig determines their irreplaceable place inthe interspecies transmission of influenza virus. So, besides its severe veterinary importance,swine influenza also poses serious public health threats. Folium syringae is the dry leave ofSyringa oblata Lindl and Syringa dilatata Nakai and Syringa vulgaris L., it belongs to Syringa ofOleaceae. Its leaves have been used extensively as one of the traditional Chinese folk herbs andpossess significant broad-spectrumantimicrobial and antiviral effects. However, no information isavailable on their potential antiviral activities against swine influenza virus. In the present paper,therefore, we investigated the antiviral activity of ethanol extracts from Folium syringae leaves(EFFL), against swine influenza virus type A in vitro and in vivo, and the effect of EFFL oncytokines in BALB/c mice infected by swine influenza virus, to provide theoretical basis for thefurther research and clinical application of Folium syringae.In an in vitro assay, we firstly determined the toxicity of EFFL and AMA to MDCK cells toidentify the half of the toxic drug concentrations (TC50) and the largest nontoxic concentrations(TC0), and then observed the antiviral efficiency of different drug-added ways against swineinfluenza virus A/swine/Tianjing/14/2009(H1N1) by the MTT method and CPE method. Theexperiment results indicated that the TC0and the TC50were250μg/mL and759.98±9.42μg/mL.Within the scope of biggest nontoxic concentration, the TI of the EFFL was13.52,6.82,15.76,16.30μg/mL separately under different drug-added ways.In an in vivo assay, the toxicity of EFFL to mouse was firstly determined to assure the densityof innocuity. Mice were infected with SIV through nasal cavity to make model mice. The majorcriteria for evaluating the effects of EFFL on mice infected with SIV including influence on thebody weight, lung index, viral titers and pathological changes in the lung. Also, the contents of cytokine IL-6, IL-10, TNF-α and IFN-γ in the serum were observed using ELISA to research on theinfluence of EFFL. The results showed that oral treatment of the EFFL at the largest concentrationof1000mg/kg/d did not lead to toxic effects in mice. And the EFFL could significantly decreasethe lung index, viral titers and pathological changes in the lung. The concentration of TNF-α, IL-6and IL-10in model group was higher than those of control group (P<0.05) after the mice wereinfected by swine influenza virus, and the concentration of IFN-γ was decreased (P<0.05).Compared with model group, the levels of IL-10and IFN-γ in EFFL group were dramaticallyhigher (P<0.05), and the levels of TNF-α and IL-6were lower (P<0.05).