METHODS: Lignosus rhinocerotis, Pleurotus giganteus, Hericium erinaceus, Schizophyllum commune and Ganoderma lucidium were selected for evaluation of their in-vitro anti-dengue virus serotype 2 (DENV-2) activities. Hot aqueous extracts (HAEs), ethanol extracts (EEs), hexane soluble extracts (HSEs), ethyl acetate soluble extracts (ESEs) and aqueous soluble extracts (ASEs) were prepared from the selected mushrooms. The cytotoxic effects of the extracts were evaluated by the MTT assay. The anti-DENV-2 activities of the extracts were evaluated in three different assays: simultaneous, attachment and penetration assays were perfomed using plaque reduction assays and RT-qPCR assays. The effect of the addition time on viral replication was assessed by the time of addition assay, and a virucidal assay was carried out to evaluate the direct effect of each mushroom extract on DENV-2. The chemical composition of glucans, and the protein and phenolic acid contents in the extracts were estimated.
RESULTS: We found that the HAEs and ASEs of L. rhinocerotis, P. giganteus, H. erinaceus and S. commune were the least toxic to Vero cells and showed very prominent anti-DENV2 activity. The 50% inhibitory concentration (IC50) values of the ASEs ranged between 399.2-637.9 μg/ml, while for the HAEs the range was 312.9-680.6 μg/ml during simultaneous treatment. Significant anti-dengue activity was also detected in the penetration assay of ASEs (IC50: 226.3-315.4 μg/ml) and HAEs (IC50: 943.1-2080.2 μg/ml). Similarly, we observed a marked reduction in the expression levels of the ENV and NS5 genes in the simultaneous and penetration assays of the ASEs and HAEs. Time-of-addition experiments showed that the highest percent of anti-DENV2 activity was observed when the mushroom extracts were added immediately after virus adsorption. None of the extracts exhibited virucidal effect. Chemical composition analysis showed that the major components in the mushroom HAEs and ASEs were glucan (beta D-glucan) and proteins, however, there was no significant correlation between the anti-dengue activity and the concentration of glucans and proteins.
CONCLUSION: These findings demonstrated the potential of mushroom extracts as anti-dengue therapeutic agents with less toxic effects.
METHODS: Geraniin was prepared from Nephelium lappaceum rind by reverse phase C-18 column chromatography. Cytotoxicity of geraniin towards Vero cells was evaluated using MTT assay while IC50 value was determined by plaque reduction assay. The mode-of-action of geraniin was characterized using the virucidal, attachment, penetration and the time-of-addition assays'. Docking experiments with geraniin molecule and the DENV envelope (E) protein was also performed. Finally, recombinant E Domain III (rE-DIII) protein was produced to physiologically test the binding of geraniin to DENV-2 E-DIII protein, through ELISA competitive binding assay.
RESULTS: Cytotoxicity assay confirmed that geraniin was not toxic to Vero cells, even at the highest concentration tested. The compound exhibited DENV-2 plaque formation inhibition, with an IC50 of 1.75 μM. We further revealed that geraniin reduced viral infectivity and inhibited DENV-2 from attaching to the cells but had little effect on its penetration. Geraniin was observed to be most effective when added at the early stage of DENV-2 infection. Docking experiments showed that geraniin binds to DENV E protein, specifically at the DIII region, while the ELISA competitive binding assay confirmed geraniin's interaction with rE-DIII with high affinity.
CONCLUSIONS: Geraniin from the rind of Nephelium lappaceum has antiviral activity against DENV-2. It is postulated that the compound inhibits viral attachment by binding to the E-DIII protein and interferes with the initial cell-virus interaction. Our results demonstrate that geraniin has the potential to be developed into an effective antiviral treatment, particularly for early phase dengue viral infection.