Antiviral activity of triptolide on herpes simplex virus in vitro

BACKGROUND: Herpes simplex virus‐type 1 (HSV‐1) can cause diseases, especially amongst neonates and immunocompromised hosts. Hence, developing a novel anti‐HSV‐1 drug with low‐level toxicity is vital. Triptolide (TP), a diterpenoid triepoxide is a natural product with range of bioactivity qualities. METHODS: In this study, viral infection was assessed in different phases of the HSV‐1 replication cycle on A549 cells, using various assays, such as adsorption inhibition assay, penetration inhibition assay, time‐of‐addition assay, and quantitative polymerase chain reaction (qPCR). RESULTS: The results indicate that TP can effectively inhibit HSV‐1 infection in the lowest range of concentration. TP exhibited significant inhibitory effect on HSV‐1 plaque formation, with 50% effective concentration (EC50) of 0.05 µM. Furthermore, the time‐of‐addition assay suggests that TP has viral inhibitory effects when it was added less than 8 h postinfection (h.p.i.). This result is further confirmed by decline in the expression viral immediate‐early genes (ICP4, ICP22, and ICP27) in 6 h.p.i in the TP‐treated group compared to the control group, evaluated by real‐time qPCR. The Western blotting result was also consistent with the previous findings, which confirms that TP can positively affect ICP4 during HSV‐1 infection. CONCLUSIONS: The TP also showed antiviral activity against HSV‐1. This dose‐dependent activity is an indication of a particular cellular component, rather than cytotoxicity that has mediated its function. Finally, the result suggest a new approach for an effective treatment option of the HSV‐1 infections.