Antiviral effect of Inonotus obliquus (Pers.:Fr.) Pilat extract against herpes simplex virus type 1 in vitro

The anti-herpes simplex virus type 1 (anti-HSV-1) activity of polypore fungus Inonotus obliquus (Pers.:Fr.) Pilat extract was studied in vitro.

The fungus material was obtained from Pakuso LLC, Finland and collected from birch trees grown in Finland above the Arctic Circle. The extract was obtained by treating the certified fungus material with an alcohol-water extractant that was at the end stripped to dryness. The dry extract was then dissolved into water.

For the experiment, wild type HSV-1 strain F was incubated with I. obliquus extract or mock control i.e. water undergone the same preparation process as the I. obliquus extract. Vero cell cultures in 24-well plates were infected with the virus and incubated. Infected cells were identified by immunoperoxidase staining. The effect of I. obliquus extract on the host cell viability was tested by a resazurin assay. Vero cells were cultured in a 96-well plate in the presence of I. obliquus extract or mock control in the concentrations of 5.6 × 10^-6 – 7.5 × 10⁰ mg/ml. Wells containing no cells filled with cell culture media were used as a control. Triton X-100 was used as a positive control for cytotoxicity at two concentrations.

I. obliquus extract in the concentrations of 4.5 × 10^-5 – 7.5 × 10⁰ mg/ml had clear anti-HSV-1 effect. Extract concentration of 2.25 × 10^-5 mg/ml and lower did no longer have anti-HSV-1 effect. Mock control had no anti-HSV-1 effect. I. obliquus extract showed viability of Vero cells by 8.1%, 15.5% and 55.8% respectively at the concentrations of 7.5 mg/ml, 3.75 mg/ml and 1.88 mg/ml. Lower concentrations possessed no cytotoxic effect. Mock control showed no cytotoxicity to the Vero cells.

The results demonstrate the anti-HSV-1 effect of I. obliquus, indicating need for further experiments to determine the active compounds and the mechanism of action.