Aqueous and ethanol extracts of propolis were analysed phytochemically and examined for their antiviral activity in vitro. Different polyphenols, flavonoids and phenylcarboxylic acids were identified as major constituents. The antiviral effect of propolis extracts and selected constituents, e.g. caffeic acid (1), p-coumaric acid (2), benzoic acid (3), galangin (4), pinocembrin (5) and chrysin (6) against herpes simplex virus type 1 (HSV-1) was analysed in cell culture. The 50% inhibitory concentration (IC(50)) of aqueous and ethanol propolis extracts for HSV-1 plaque formation was determined at 0.0004% and 0.000035%, respectively. Both propolis extracts exhibited high levels of antiviral activity against HSV-1 in viral suspension tests, plaque formation was significantly reduced by >98%. In order to determine the mode of antiviral action of propolis, the extracts were added at different times during the viral infection cycle. Both propolis extracts exhibited high anti-HSV-1 activity when the viruses were pretreated with these drugs prior to infection. Among the analysed compounds, only galangin and chrysin displayed some antiviral activity. However, the extracts containing many different components exhibited significantly higher antiherpetic effects as well as higher selectivity indices than single isolated constituents. Propolis extracts might be suitable for topical application against herpes infection.

Aqueous extracts from species of the Lamiaceae family were examined for their antiviral activity against Herpes simplex virus (HSV). Extracts from lemon balm (Melissa officinalis), peppermint (Mentha x piperita), prunella (Prunella vulgaris), rosemary (Rosmarinus officinalis), sage (Salvia officinalis) and thyme (Thymus vulgaris) were screened. Their inhibitory activity against Herpes simplex virus type 1 (HSV-1), type 2 (HSV-2) and an acyclovir-resistant strain of HSV-1 (ACV (res)) was tested in vitro on RC-37 cells in a plaque reduction assay. The 50% inhibitory concentrations (IC (50)) of the extracts for HSV plaque formation were determined in dose-response studies. All test compounds showed a high antiviral activity against HSV-1, HSV-2 and ACV (res). In order to identify the mode of antiviral action, the extracts were added to the cells or viruses at different stages of infection. Both types of Herpes virus including ACV (res) were considerably neutralized after treatment with the extracts prior to infection. At maximum non-cytotoxic concentrations of the extracts, plaque formation was significantly reduced by > 90% for HSV-1 and HSV-2 and > 85% for ACV (res). In time-response studies over a period of 2 hours, a clearly time-dependent activity was demonstrated. These results indicate that the extracts affect HSV before adsorption, but have no effect on the intracellular virus replication. Therefore, the extracts exert their antiviral effect on free HSV and offer a chance to use them for topical therapeutic application against recurrent HERPES infections.

Aqueous extracts from Lamiaceae can drastically and rapidly reduce the infectivity of HIV-1 virions at non-cytotoxic concentrations. An extract-induced enhancement of the virion's density prior to its surface engagement appears to be the most likely mode of action. By harbouring also a strong activity against herpes simplex virus type 2, these extracts may provide a basis for the development of novel virucidal topical microbicides.

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Background: Extracts of medicinal plants are increasingly of interest as novel drugs for antimicrobial and antiviral agents, since microorganisms might develop resistance to commonly used antimicrobial or antiviral agents. Materials and Methods: Ethanolic extracts from Lamiaceae plants prunella, peppermint, rosemary and thyme were phytochemically characterised. The inhibitory activity of four 20% ethanolic plant extracts and four 80% ethanolic extracts against herpes simplex virus (HSV) strains was tested in cell culture. Results: Rosmarinic acid, a typical compound in Lamiaceae species, was identified in the extracts except for thyme 20% ethanolic extract. In addition, some other phenolic compounds such as apigenin- and luteolin-derivatives were identified in different amounts. All extracts exhibited high and concentration-dependent levels of antiviral activity against free acyclovir-sensitive and acyclovir-resistant HSV-1 strains with 50% inhibitory concentrations of 0.05–0.82 μg/ml. Mechanistically, exposure of free virions as well as host cells to prunella and peppermint 80% ethanolic extracts at maximum non-cytotoxic concentrations prior to infection reduced plaque formation drastically. Thus, both extracts revealed a dual mode of action similar to aqueous lemon balm extracts. Conclusions: Since infectivity of acyclovir-susceptible and acyclovir-resistant HSV strains was significantly reduced with Lamiaceae extracts, the results obtained indicate that ethanolic plant extracts affected herpesvirus prior to and during adsorption and in a different way than acyclovir. Based on its dual mode of action, e.g. antiviral effect against free virions and blocking virus attachment to host cells, prunella and peppermint 80% ethanolic extracts are promising antiviral agents in recurrent herpes labialis for topical therapeutic applications.