Evaluation of the anti-neuraminidase activity of the traditional Chinese medicines and determination of the anti-influenza A virus effects of the neuraminidase inhibitory TCMs in vitro and in vivo

Five out of 439 TCMs, Duchesnea indica (Andr.) Focke [Fragaria indica Andr.], Liquidambar formosana Hance, Lithospermum erythrorhizon Sieb. et Zucc., Melia toosendan Sieb. et Zucc., and Prunlla vulgaris L. exhibited strong inhibitory activities to NA. The viral inhibitory activity of these NA inhibiting TCMs were tested in H1N1 viral infected MDCK cells. These TCMs protect cells from viral induced CPE and reduced the virus load in MDCK cells in a dose-dependent manner as showed by the cellular NA activity measurement. Neuraminidase (NA) inhibitors are currently the most effective drugs to treat influenza A viruses infection. Many traditional Chinese medicines (TCMs) have been used in the clinics to treat influenza. The anti-viral mechanisms of these TCMs and their inhibitory effects towards NA need to be systematically tested. To evaluate the anti-NA activity of the TCMs and the anti-influenza A virus effects of the NA inhibitory TCMs in vitro and in vivo. We tested the inhibitory activity of water extracts from 439 TCMs towards NA. The in vitro anti-influenza virus activities of the 5 TCMs were evaluated using the strain A/California/7/2009 (H1N1) NYMC X-179A of influenza A virus. A randomly selected TCM with NA inhibitory activity, Melia toosendan extract, was further evaluated using a mouse model infected with influenza A virus. Five TCMs, Duchesnea indica (Andr.) Focke [Fragaria indica Andr.], Liquidambar formosana Hance., Lithospermum erythrorhizon Sieb. et Zucc., Melia toosendan Sieb. et Zucc., and Prunella vulgaris L., exerted potent inhibitory activity towards NA. These TCMs in the range of 25–250μg/mL had the ability to reduce virus-induced cytopathic effect (CPE) and the virus yield in MDCK cells. Melia toosendan significantly reduced death rate and prolonged mean day to death (MDD) of the viral infected mice. This study describes five TCMs exerted strong inhibitory activities towards NA, and exhibited antiviral effect against influenza A virus by reducing viral reproduction and reduced CPE of the viral infected cells. Melia toosendan, significantly reduced death rate and prolonged survival of the H1N1 viral infected mice.