Anti-herpes simplex virus activities of monogalactosyl diglyceride and digalactosyl diglyceride from Clinacanthus nutans, a traditional Thai herbal medicine

Objective: To evaluate the monogalactosyl diglyceride (MGDG) and digalactosyl diglyceride (DGDG) from Clinacanthus nutans (C. nutans) for their in vitro antiviral activities against herpes simplex virus type 1 (HSV-1) and type 2 (HSV-2) by plaque reduction assay. 

Methods: MGDG and DGDG were extracted with chloroform from C. nutans leaves. MGDG and DGDG were separated from chloroform crude extract using column chromatography, characterized by thin layer chromatography and quantified by high performance liquid chromatography. The anti HSV-1 and 2 activity against pre-treatment and post-treatment of the compounds was evaluated using plaque reduction assay. The cytotoxicity of the extract and the compounds on Vero cells were performed by MTT assay. 

Results: MGDG and DGDG obtained by column chromatography showed identical profiles as standard MGDG and standard DGDG using thin layer chromatography and high performance liquid chromatography. MGDG and DGDG from C. nutans showed 100% inhibition of HSV-1 replication at the post step of infection at noncytotoxic concentration with IC₅₀ values of 36.00 and 40.00 μg/mL, and HSV-2 at 41.00 and 43.20 μg/mL, respectively. Moreover, MGDG and DGDG from C. nutans were demonstrated to have anti-herpes simplex activity at the same level as standard synthetic compounds. In contrast, pre-treatment of Vero cells with MGDG and DGDG before HSV-1 and HSV-2 infection did not show inhibitory effect against these viruses. MGDG and DGDG exhibited antiviral activity against HSV-1 with selectivity index of 26.00 and 23.00 and HSV-2 of 23.30 and 21.30. 

Conclusions: MGDG and DGDG from C. nutans, a traditional Thai herbal medicine illustrated inhibitory activity against HSV-1 and HSV-2, probably by inhibiting the late stage of multiplication, suggesting their promising use as anti-HSV agents.