Biological activity of Gunnera tinctoria, an invasive plant in the island of S. Miguel (Azores)

Gunnera tinctoria (Mol.) Mirb. is a Halogaracea originary from South America, which was introduced in the island of S. Miguel (Azores). An ornamental plant, it escaped from the Furnas botanical garden in the 1960s and has been slowly invading the central area of the island [1]. This plant has been the object of preliminary work in our laboratory [2], and there are reports about biological activities detected in another species belonging to the same genus [3].

Dichloromethane and methanol leaf extracts of G. tinctoria were prepared either by soxhlet extraction (hot – CHCl₂ and hot – MeOH, respectively), or at room temperature (cold – CHCl₂ and cold – MeOH). The extracts were screened both for antibacterial activity against Pseudomonas aeruginosa, Bacillus subtilis, Escherichia coli and Micrococcus luteus, and for antitumour activity against HeLa cell line.

The only antibacterial activity detected was from the hot – CHCl₂ extract against Micrococcus luteus (EC₅₀ =169.15µg/mL). All extracts were active against HeLa tumour cell line, both in antiproliferative and in cytotoxycity assays. The extract which exhibited higher activity was hot – MeOH, with EC₅₀ values of 25.3 and 49.5µg/mL for antiproliferative and cytotoxicity assays, respectively. Soxhlet extraction yielded better results than cold extraction, suggesting that the active compound(s) involved are not particularly heat labile. The results obtained are promising and further work will be carried out to identify the molecules responsible for the effects detected.

References: 1. Sjögren, E. (1984), Azores Flowers. Direcção Regional do Turismo, Horta. 2. Medeiros, J., Macedo, F.W. et al. (1999), Açoreana 9: 55–61. 3. Drewes, S.E., Khan, F., et al. (2005), Phytochemistry 66: 1812–1816.