Citotoxic activity evaluation of essential oils and nanoemulsions of Drimys angustifolia and D. brasiliensis on human glioblastoma (U-138 MG) and human bladder carcinoma (T24) cell lines in vitro

The species Drimys angustifolia Miers and D. brasiliensis Miers, commonly known as "casca-de-anta", have in their leaves essential oils that can confer cytotoxic effects. In this study, we evaluated the citotoxic effects of the volatile oils from these two species. We also proposed a nanoemulsion formulation for each of the species and assessed the in vitro cytotoxicity on U-138 MG (human glioblastoma) and T24 (human bladder carcinoma) cell lines. The plant chemical composition was evaluated by gas chromatography coupled to mass spectrometer. Furthermore, the nanoemulsions were prepared and characterized. Our results showed that; bicyclogermacrene (19.6%) and cyclocolorenone (18.2%) were the most abundant for the D angustifolia oil and D brasiliensis oil, respectively. Both nanoemulsions, D angustifolia and D brasiliensis appeared macroscopically homogeneous and opalescent bluish liquids, with nanometric mean diameters of 168 nm for D brasiliensis and 181 nm for D angustifolia. The polydispersity indices were below 0.10, with an acid pH of 4.7-6.3, and negative zeta potentials about -34 mV. The results of transmission electron microscopy showed that droplets are present in the nanometer range. Only the D brasiliensis oil was efficient in reducing the cell viability of both U-138 MG (42.5%+/- 7.0 and 67.8%+/- 7.8) and T24 (33.2%+/- 2.8, 60.3%+/- 1.6 and 80.5%+/- 8.8) cell lines, as assessed by MTT assay. Noteworthy, similar results were obtained with cell counting. Finally, D brasiliensis oil incubation caused an increase of annexin-V and propidium iodite population, according to evaluation by cytometry analysis, what is characteristic of late apoptosis. The results presented herein lead us to consider the potential therapeutic effects of the essential oils and nanoformulations as novel strategies to inhibit tumor growth.