Screening of neuraminidase inhibitory activities of some medicinal plants traditionally used in Lingnan Chinese medicines

Background: Neuraminidase (NA) is one of the key surface protein of the influenza virus, and has been established as a primary drug target for anti-influenza therapies. This study aimed to screen bioactive herbal extracts from some medicinal plants traditionally used in Lingnan Chinese Medicines by NA activity high-throughput screening assay. Methods: One hundred ninety herbal extracts from 95 medicinal plants collected in Guangzhou were screened for their potential inhibitory activities against A (H1N1) influenza neuraminidase, and the most active extracts were further evaluated for their anti-influenza virus activities using virus-induced cytopathic effect (CPE). Results: Among the tested 190 herbal extracts, 14 extracts inhibited significantly NA activity (IC50 < 40 mu g/mL), and the extracts 1-5, which were obtained from Amomurn villosum Lour, Melaphis chinensis (Bell) Baker, Sanguisorba officinalis and Flos Caryophylli, showed potent inhibitory activity against NA with IC50 values ranging from 4.1 to 9.6 mu g/mL. Moreover, the most bioactive extracts 1-5 were found to protect MDCK cells from A (H1N1) influenza virus infection with very low cytotoxicity to the host cells (EC50 values ranged from 1.8 to 14.1 mu g/mL, CC50 values ranged from 97.0 to 779.2 mu g/mL, SI values ranged from 14 to 438). In addition, quantitative RT-PCR analysis showed that the extracts 1-5 inhibited viral RNA synthesis in a dose-dependent manner. Conclusion: We performed in vitro screening of anti-neuraminidase activities of herbal extracts from medicinal plants used in Lingnan Chinese Medicines, and the results indicate that some bioactive extracts are worth further studies to identify the bioactive components responsible for anti-influenza virus activities, to elucidate their modes of action and finally determine their clinical potentials.