Mexican Oregano ( Schauer and Gray) Essential Oils Induce Cell Death by Apoptosis in Promastigotes.

Leishmaniasis is a neglected vector-borne disease; there are different manifestations of the diseases and species involved, and cutaneous leishmaniasis caused by is the most prevalent in Mexico. Currently, the drugs available for the treatment of leishmaniasis are toxic, expensive, and often ineffective; therefore, it is imperative to carry out research and development of new therapeutic alternatives, with natural products being an attractive option. In particular, oregano is a plant with worldwide distribution; in Mexico, two species: Schauer and Gray are endemic. Both essential oils (EO's) have been reported to have antimicrobial activity attributed to their main components, thymol and carvacrol. In this research, the leishmanicidal effect and mechanism of cell death induced by EO, EO, thymol, and carvacrol in promastigotes were determined in vitro. Additionally, the cytotoxic activity in mammalian cells was evaluated. EO presented higher leishmanicidal activity (IC = 41.78 µg/mL) than EO (IC = 77.90 µg/mL). Thymol and carvacrol were the major components of both Mexican oregano EO's. Thymol presented higher leishmanial inhibitory activity (IC = 22.39 µg/mL), above that of carvacrol (IC = 61.52 µg/mL). All the EO's and compounds evaluated presented lower cytotoxic activity than the reference drug; thymol was the compound with the best selectivity index (SI). In all cases, apoptosis was identified as the main mechanism of death induced in the parasites. The leishmanicidal capacity of the Mexican oregano EO is an accessible and affordable alternative that can be further explored.