Chemical composition of Ocimum canum Sims. essential oil and the antimicrobial, antiprotozoal and ultrastructural alterations it induces in Leishmania amazonensis promastigotes

The complications involved in current leishmaniasis treatment indicate the urgent need for new therapeutic strategies. In research into new compounds from natural products that possess antileishmanial activity, Ocimum canum species from the Brazilian Amazon have been little studied. Therefore, the present study aimed to evaluate the chemical composition and antileishmanial activity of O. canum essential oil and the ultrastructural alterations it induced in Leishmania amazonensis. Preliminary antimicrobial, antitrypanosomal and in vitro cytotoxic activity were also analyzed. Chemical constituents assessed by gas chromatography-mass spectrometry analyzes identified thymol (42.15%), p-cymene (21.17%) and γ-terpinene (19.81%) as major compounds. The O. canum essential oil displayed antimicrobial activity against Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa. Antiprotozoal activity showed IC50 of 17.4 μg/mL and 13.1 μg/mL for L. amazonensis promastigote and intracellular amastigote, respectively, and 60.0 μg/mL for Trypanosoma cruzi. Selectivity index showed selectivity for L. amazonensis pormastigote (18.1) and amastigote intracellular (24.0), but not for T. cruzi (5.2) when compared with cytotoxicity against BALB/c peritoneal macrophages (CC50 315.3 μg/mL). The ultrastructural alterations observed in L. amazonensis treated with O. canum essential oil were autophagosome-like structures, which were multivesicular and had lipid bodies, discontinuity of the nucleus membrane and exocytic activity by the flagellar pocket. The results evidenced the rich chemical composition of O. canum essential oil, as well its antileishmanial activity and high selectivity index for these parasites, although not for cells, revealing its potential for further in vivo studies.