Antileishmanial apoptotic activity of Nigella sativa L. essential oil and thymoquinone triggers on Leishmania tropica

Abstract

Nigella sativa L., commonly called Black cumin, is well-known in folk medicine and numerous studies have shown its various pharmacological activities. In this study, we estimated the cytotoxic effects of N. sativa essential oil (NEO) and its major bioactive component Thymoquinone (TQ) on Leishmania tropica promastigotes that cause cutaneous leishmanias, and also observed the programmed cell death features. The extraction of NEO was done by hydro-distillation and analyzed by Gas Chromatography-Mass Spectrometry (GC-MS). Antileishmanial activity of NEO and TQ was determined using 3-(4.5-dimethylthiazol-2-yl)-2.5-diphenyl tetrazolium bromide (MTT) assay and the obtained results are expressed as 50% inhibitory concentration (IC₅₀). The leishmanicidal activity of NEO and TQ was mediated via apoptosis as evidenced by in situ labelling of DNA fragments using terminal deoxyribonucleotidyltransferase-mediated dUTP nick end labelling (TUNEL) and cell cycle arrest at sub G₀/G₁ phase. The IC₅₀ values were 5 µg/mL and 1.3 µg/mL, respectively. We noted a significant increase in DNA fragmentation in treated parasites with IC₅₀ of both NEO and TQ as well as a cell cycle arrest. These results revealed that NEO and TQ possess potential antileishmanial activity that mediated high possibility by programmed cell death.