Evaluation of the anti-herpes simplex virus activity of Thymus longicaulis L. (Lamiaceae)

The genus Thymus is one of the eight most important genera within the Lamiaceae family, with regard to its number of species. Thyme is a perennial herbaceous plant, indigenous to central and southern Europe, which is widely cultivated for its use as a tea, spice, and herbal medicine. Its leaf is listed both in the German and British Herbal Pharmacopoeias, and it has been used as a stomachic, carminative, diuretic, urinary disinfectant, and vermifuge.

Herpes simplex viruses (HSV) are ubiquitous pathogens that cause a variety of diseases ranging in severity from mild to severe. Following a primary infection, HSV establishes a latent life-long infection within the nerve cells of the trigeminal ganglia, with periodic reactivations.

Continuing our chemotaxonomic analyses of the Greek flora of the Lamiaceae family and the search for pharmacologically interesting compounds from these plants, here we evaluate the antiviral activity of the aerial parts of T. longicaulis. Specifically, we assess their virucidal activity against herpes simplex virus, type 1 (HSV-1), as well as their ability to inhibit the attachment and penetration steps of the HSV-1 infection cycle.

Air-dried, powdered aerial parts of the above mentioned plant were extracted at room temperature with a series of solvents of increasing polarity, i.e. petroleum ether, CH₂Cl₂, MeOH, 1:1 mixture of MeOH-H₂O and H₂O. The dried extracts were dissolved either in DMSO or in sterile deionised and distilled water and they were tested for their above-described anti-HSV-1 activities, i.e. virucidal action and inhibition of virus entry. Significant anti-HSV activities were found in the dichloromethane and the methanolic extracts, which were subsequently subjected to bioguided chromatographic fractionation. The purity of five chromatographic fractions, possessing anti-HSV activities, was assessed by chromatography/spectroscopy and they were found to consist of pure compounds. We are in the process of analyzing the structures of these compounds, as well as further evaluating their mechanism of action at the molecular level.