Antioxidant and antiproliferative activities of essential oils of some wild Portuguese Thymus
In the present work, the capacity for scavenging peroxyl and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radicals, of the essential oils (EOs) of Thymus caespititius, T. mastichina, T. pulegioides, T. villosus and Thymbra capitata, collected in different regions of Portugal, was evaluated. The antiproliferative activity of the same EOs on the THP-1 leukemia cell line was also studied. The EO of T. caespititius from Terceira and Faial, and T. capitata EOs, in which thymol (42%) and carvacrol (50 – 68%) predominated, presented the best capacity for scavenging ABTS radicals [27.3, 25.8 and 25.2 mmol Trolox Equivalent (TE)/g EO, respectively]. These EOs were also the best for scavenging peroxyl radicals (182.8 – 190.6 mmol TE)/g) but along with those obtained from T. mastichina and T. pulegioides (178.4 and 179.4 mmol TE)/g, respectively). 1,8-Cineole (47%) and geraniol (33%) predominated in T. mastichina and T. pulegioides EOs, respectively, although thymol had also been detected in relative high amounts (14 and 12%, respectively). Essential oils reduced cell viability of THP-1 in a dose-dependent manner. Only 66% of THP-1 cells survived with 10 mg/mL of the EO of T. caespititius from Pico, after 24h of exposure. In the same time interval, for higher concentrations (> 400 mg/mL), the EOs from T. mastichina, T. pulegiodes, T. caespititius from Praia do Cortiço (Azores) and T. villosus had the lowest citotoxicity. 1,8-Cineole, geraniol, a-terpineol and linalool were the main components of these EOs. Only higher percentages of thymol and carvacrol were able to prevent the cell proliferation.
Acknowledgements: This study was partially funded by FCT, under PestOE/EQB/LA0023/2011