Abstract
This study rated antiviral activity of Scutellaria baicalensis Georgi (S. baicalensis) extracts against influenza A virus subtypes, for example, pandemic 2009 H1N1, seasonal H1N1 and H3N2. Ethyl acetate (EtOAc) and chloroform extracts inhibited in vitro neuraminidase (NA) enzymatic activity and viral replication more than methanol (MeOH) extract. EtOAc extract demonstrated NA inhibition IC50 values ranging from 73.16 to 487.40 μg/mL and plaque reduction IC50 values ranging from 23.7 to 27.4 μg/mL. Chloroform extract showed antiviral activities with plaque reduction IC50 values ranging from 14.16 to 41.49 μg/mL Time-of-addition assay indicated that EtOAc and chloroform extracts also significantly inhibited virus yields after infection. HPLC analysis demonstrated that baicalin was dominant in the MeOH extract; baicalein and chrysin were rich in the EtOAc and chloroform extracts. Molecular simulation revealed baicalein hydrogen bonding with Glu277 as well as hydrophobic and Van der Waals interactions with Ile222, Arg224, Ser246, and Tyr347 in NA1 active sites of NA1. Baicalein inhibited in vitro replication of influenza A viruses pandemic 2009 H1N1 (IC50 = 0.018 μM) and seasonal 2007 H1N1 using plaque reduction assays. A combination of low-dose baicalein with other anti-influenza agents could be applicable for development of alternative remedies treating influenza A virus infection.
Highlights
Influenza A virus, a member of the Orthomyxoviridae family, is an enveloped virus containing eight segmented, negativesense, single-stranded RNAs [1, 2]
To screen inhibitory effects of S. baicalensis extracts on NA enzymatic activity, fluorometric activity assay of NA with MUNANA substrate indicated NA enzymatic activity of pandemic 2009 and seasonal 2007 H1N1 influenza A viruses by virus titer-dependent manner (Figure 1)
MeOH, EtOAc, and chloroform extracts of S. baicalensis were prepared to test their inhibitory effects on NA activity of five variants: pandemic 2009 H1N1, seasonal 2007 H1N1, 2009 H1N1, 2009 H3N2, and PR8 H1N1 influenza A viruses (Table 1)
Summary
Influenza A virus, a member of the Orthomyxoviridae family, is an enveloped virus containing eight segmented, negativesense, single-stranded RNAs [1, 2]. HA, NA, and M2 locate on the outer side of a viral envelope and M1 on the inner side. Of these envelope proteins, HA contains the receptor-binding site, being responsible for virus fusion and infectivity [3]. NA digests sialic acid on the cell surface, resulting in release of virus particles and spread of the virus. Envelope proteins (HA, NA, and M2) play key roles in viral infectivity, making them prime targets for prophylaxis and therapeutic anti-influenza A virus drugs. Oseltamivirresistant and amantadine-resistant variants emerge and are identified in several countries [4,5,6,7,8,9], creating a need to develop new anti-influenza compounds
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