Cytotoxic effect of Croton sphaerogynus extracts against Rhipicephalus microplus cell line

Croton (Euphorbiaceae) comprises approximately 1,300 species in tropical regions. In almost all Brazilian ecosystems Croton species occur, and some are used in folk medicine for various purposes [1]. The diversity of medicinal uses of Croton species is related to a wide diversity of secondary metabolites. The cattle tick Rhipicephalus microplus is one of the economically most damaging livestock ectoparasites, and its widespread resistance to acaricides is a considerable challenge to its control. The aim of this study was to evaluate the cytotoxic effect of hexanic fraction of C. sphaerogynus (HEF) against the embryonic cells of Rhipicephalus microplus (strain BME26). Leaf material was collected in Itanhaém, São Paulo, dried, powdered and 1 kg was subjected to maceration in ethanol for seven days. Crude extract was fractionated using methanol and hexane, in order to obtain a fraction rich in diterpenes (HEF). Tetrazolium dye MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide) was used to evaluate the cytotoxicity of different HEF concentrations. Percentage of viable cells treated with HEF was normalized to the untreated cells, which were considered to be 100% viable. At a concentration of 500 µg/mL HEF cell viability was 12.16%. At the lowest concentration tested (0.975 µg/mL) 60.05% of viable cell was observed. Morphological features of the treated cells suggested apoptosis as the mode of action. These data demonstrated that HEF can lead to cell death following a polynomial dose-response curve (IC₅₀ 103.7 and 0.63 µg/mL, respectively). Croton species are potential sources for the discovery of natural products with acaricidal activity.

Acknowledgements: FAPESP (2012/10079 – 0), CNPq and CAPES.

References:

[1] Salatino A, Salatino MLF, Negri G. Traditional uses, chemistry and pharmacology of Croton species (Euphorbiaceae). J Braz Chem Soc 2007; 18: 11 – 33