The Potential Inhibitory Effect of Sambucus Nigra Fruit on Early Replication of Influenza Virus

Influenza is considered as a serious threat to human and animal health worldwide. In recent years, with the rise of drug-resistant strains, antiviral property of herb natural components with fewer side effects is of great importance. In this study, the potential antiviral activity of Sambucus nigra fruit was evaluated in human epithelium cell (A549) cultures infected with influenza virus. The aqueous extract of Sambucus nigra fruit was prepared and the cytotoxic concentration of the extract on A549 cells was determined. Subsequently, the 50 percent inhibitory concentration (IC50) of various herbal extract concentrations for inhibiting the replication of influenza virus and the selective index (SI) were assessed following pre-treatment (before the virus attachment to cells or direct effect) and post-treatment (after virus absorption to cells or indirect effect) procedures. Inhibitory effect of the herb on virus replication was examined via using virus titration and quantitative real time reverse transcription polymerase chain reaction (real time RT-PCR). The concentration of 82.6 μg/ml was the threshold dose of the substance that did not cause a cytotoxic effect against the cells. The estimated selective index of the extract before cellular attachment (15.10 μg/ml), increased viral titer as well as synthesized viral nucleoprotein RNAs indicating that the herb had no direct inhibitory effects on viral hemagglutinin activity. In post-treatment, the higher estimated selective index, a significant decrease was seen in virus titer and viral nucleoprotein copy numbers confirming that the herb inhibited virion budding and release activities. The results suggest that Sambucus nigra treatment of the influenza virus infected-human epithelial cells may affect either inhibition of virus particle release or involving in cellular lipid raft function. Mechanism of this interaction will be investigated in future studies.