Dioscin's antiviral effect in vitro
Highlights
► Dioscin has low toxicity to 293 and HepG2 2.215 cell lines. ► Dioscin can inhibit the early stage of adenovirus infection. ► Dioscin can attenuate adenovirus infection by reducing the expression level of viral receptors. ► Dioscin can inhibit VSV infection during its contact with cells. ► Dioscin can block the secretion level of HBsAg and HBeAg in HepG2 2.215.
Introduction
Many chemical compounds from various pharmacological medicinal plants are extensively researched not only for their potential inhibitory properties against virus invasion but also for their low toxicity in cells, such as flavonoid (Shin et al., 2005). Dioscin is a compound isolated from an extract of an air potato. Dioscin isolated in a form of a white powder which is very stable at room temperature. Its molecular weight is 869.05 Da (Fig. 1A). It is insoluble in water but resolved in ethanol. Previous report has indicated that it could induce apoptosis in some types of cancer cells. Dioscin treatment of a human esophageal cancer cell line (Kyse510) induced the production of reactive oxygen species (ROS) and mitochondrial pathway apoptosis in this cell line (Wang et al., 2012). However, role of dioscin in inhibiting the viral infection has not been addressed before. We chose 3 different viruses to test if dioscin exhibits a broad-spectrum antiviral properties: adenovirus is a non-enveloped double-stranded DNA virus, VSV is a single-stranded RNA enveloped virus and HBV is a partially double-stranded DNA enveloped virus.
Adenovirus accounts for about 10% of acute respiratory infections in children and is a frequent cause of diarrhea. Adenoviral infections affect infants and young children much more frequently than adults (Jalal et al., 2005). Adenoviral illnesses often resemble certain bacterial infections, which can be treated with antibiotics. However, antibiotics do not work against adenovirus, and there are no antiviral drugs to treat adenoviral infections. An Adenovirus Type 5 (Ad5) belongs to the adenovirus family. Ad5 enters the host cell by coxsackie-adenovirus receptor (CAR)-mediated endocytosis mechanism, and its attachment relies on its fiber protein (Nemerow and Stewart, 1999). CAR is a 48 kDa transmembrane protein, and it has two extracellular immunoglobulin-like domains located at the N-terminal moiety of the protein, a single membrane-spanning helix with a short cytoplasmic tail (Freimuth et al., 2008).
VSV belongs to Rhabdoviridae family, and VSV can cause oral disease such as mucosal vesicles and ulcers in the mouth. VSV has broad host spectrum which includes horses, cattle, pigs, sheep, goat and humans (Letchworth et al., 1999). Epidemic occurs annually or at intervals of 2–3 years in tropical and subtropical countries and at intervals of 5–10 years in temperate zones. Up to now there is no antiviral treatment available.
HBV is a member of Hepadnaviridae family. More than 300 million individuals are chronically infected with HBV worldwide (Fung and Luk, 2003). HBV infection can lead to liver related disease and hepatocellular carcinoma (HCC) (Blumberg et al., 1989). Recent study indicated that HBV can also increase the risk of pancreatic cancer (Hassan et al., 2008). Nucleoside analogs has been applied to treat chronic HBV infections (Maynard et al., 2005), however this treatment is limited to a small population and is not effective against HBV variations (Sprengers and Janssen, 2005). Currently, the combination of immune modulatory drugs and antiviral drugs (such as lamivudine, adefovir dipivoxil and tenofovir disoproxyl fumarate) is an effective way to treat HBV infections (Maynard et al., 2005, Sprengers and Janssen, 2005, Arbuthnot et al., 2005, Ristig et al., 2002). However, new more potent antiviral drugs are still need to be identified to treat chronic HBV infections. Recently, pu-erh tea extracts was shown to have anti-HBV properties with lower cytotoxicity in HepG2 2.215 cell line (Pei et al., 2011).
In this study, we investigated dioscin for its antiviral properties against several selected viruses. Our data shows that dioscin can function as a potent antiviral agent by blocking virus invasion.
Section snippets
Dioscin, cell and virus
Dioscin was extracted by liquid–solid extraction with 98% purity by HPLC. The HepG2 2.2.15 hepatoblastoma cell line that expresses stably transfected HBV genomes (Sells et al., 1987) and 293 cell line are our laboratory strains. HepG2 2.2.15 was maintained in RPMI 1640 culture media containing 10% fetal bovine serum (FBS). For the anti-HBV assay, cells were seeded in 96-well microplates at density of 104 cells per well and grown to confluence. Cells were maintained at confluence for 2–3 days
Dioscin shows little toxicity in HepG2 2.215 and 293 cells
In order to test the toxicity of dioscin in the host cells, HepG2 2.215 and 293 cells were pretreated with different concentrations of dioscin and control solvent (ethanol) for 48 h followed by MTT assay. For both HepG2 2.215 and 293 cells, the cell viability was close to 95% of the cell viability in the control group with the dioscin concentrations reaching 35 μM (Fig. 1B). This result indicated that dioscin has low toxicity effect on the cells at the concentration used in the assays. In order
Discussion
Up to date there are no reports describing dioscin's inhibitory effects against virus invasion. From the experiments presented in this paper, we can conclude that dioscin displays some antiviral effect against adenovirus, VSV and HBV. First, dioscin can inhibit the adenovirus infection when the cells were pretreated with dioscin as well as at the initial stage of virus contact. The mechanism of viral inhibition at the initial stage has not been explored in this paper. It would be of a great
Acknowledgements
We acknowledge receipt of pTopo-car and pTopo plasmids from Bei Wang. We thank Drs. Vera Stupina, Feng Gao and Xuefeng Yuan for critically reading the manuscript. This work was supported by a grant from health department of Hubei province (JX1B027).
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