Bio-active constituent from Yinqiaosan has anti-influenza and anit-inflammatory effect

Abstract

Influenza epidemics have become a major public health concern worldwide. According to the World Health Organization, the annual epidemics results in about three to five million cases of severe illness, and about 250 to 500 thousand deaths. Recurring emergence of new influenza viruses and viruses that are resistant to currently approved antiviral medications pose a critical need to explore new or alternative medications. A classical Traditional Chinese Medicine (TCM) decoction consisting of nine herbs, named Yinqiaosan (YQS, 銀翹散), has a long history for treating respiratory diseases in China. However, the efficacy of YQS has not been investigated mechanistically. In the present study, the effectiveness of YQS in treating influenza virus infection was examined. The potential mechanisms of action of two active compounds present in one of the component herbs of YQS were also investigated. Results showed that YQS increased the survival rate of the mice in an in vivo influenza virus infection model with significant reduction in lung viral titers. In order to further delineate the mechanisms of action of YQS, compounds present in a principal ingredient of YQS were examined for antiviral and immunomodulatory effects. In screening a panel of fractions extracted from YQS, forsythoside A was demonstrated to suppress the viral titers of a wide range of influenza viruses including the oseltamivir-resistant and the 2009 pandemic H1N1 viruses. Through electron microscopy, slow or abnormal viral budding events were observed upon forsythoside A treatment during influenza virus infection. Western blot analysis revealed a reduced influenza virus M1 protein expression. As previous report showed that assembly of viral components into an infectious particle required a threshold level of M1 protein, reduced M1 expression in the cells treated with forsythoside A may contribute to the virus replication suppression. On the other hand, innate immune responses provide first line protection against influenza virus infections. However, excessive responses often result in tissue damage. Cyclooxygenase (COX)-2 is an immunomodulatory factor that has been shown to play a role in the pathogenesis of influenza viruses. A previous COX-2 knock-out mice model showed that COX-2 deficiency is beneficial to the host during influenza viral infection, in which mortality was significantly reduced. Furthermore, during H5N1 infection, it has been shown that COX-2 level significantly increased and it played an essential role in coordinating the productions of inflammatory cytokines, while in another study, pharmacological inhibition of COX-2 suppressed H5N1 virus replication in primary human macrophages. In view of the roles of COX-2 during influenza virus infection, the presence of compound in YQS that reduces the influenza virus-induced COX-2 level was examined. Present results showed that jacaranone not only reduced the influenza virus-induced cyclooxygenase (COX)-2 mRNA level, it also suppressed the subsequent production of prostaglandin E2 level in primary human macrophages. At the same time, jacaranone inhibited the virus induced-activations of ERK1/2 and Akt, which are involved in the COX-2 induction. Jacaranone also suppressed, at least in part, the COX-2 mRNA level at the transcriptional level by inhibiting the nuclear translocation of NF-κB. To conclude, TCM has been recognized as an important part in complementary and alternative medicine and it is an ample source of antimicrobial drugs. The use of a mixture of herbs is the major therapeutic approach of TCM in which, the principal ingredients provide the main therapeutic actions while the others enhance the effects or diminish the side effects of the principal ones. Some components act mainly for symptomatic control. The present study not only supports the efficacy of YQS, but also gives evidences to an active antiviral compound and an immunomodulatory compound found in YQS. They may act as either principle or supporting components depending on the purpose of application. This study provides new insights on future novel drug development from the existing wisdom of TCM.