Context: Leishmaniasis is a complex disease with a broad spectrum of clinical presentations. Objective: We evaluated the anti-leishmanial effects of Nigella sativa L. (Ranunculaceae) against Leishmania tropica and Leishmania infantum with an in vitro model. Materials and methods: Antileishmanial effects of essential oil and methanolic extract of N. sativa (0-200 mg/mL) and thymoquinone (0-25 mg/mL) on promastigotes of both species and their cytotoxicity activities against murine macrophages were evaluated using the MTT assay at 24, 48, and 72 h. Moreover, their leishmanicidal effects against amastigotes were investigated in a macrophage model, for 48 and 72 h. Results: The findings showed that essential oil (L. tropica IC 50 9.3 mg/mL and L. infantum IC 50 11.7 mg/mL) and methanolic extract (L. tropica IC 50 14.8 mg/mL and L. infantum IC 50 15.7 mg/mL) of N. sativa, particularly thymoquinone (L. tropica IC 50 1.16 mg/mL and L. infantum IC 50 1.47 mg/ mL), had potent antileishmanial activity on promastigotes of both species after 72 h. In addition, essential oil (L. tropica IC 50 21.4 mg/mL and L. infantum IC 50 26.3 mg/mL), methanolic extract (L. tropica IC 50 30.8 mg/mL and L. infantum IC 50 34.6 mg/mL), and thymoquinone (L. tropica IC 50 2.1 mg/mL and L. infantum IC 50 2.6 mg/mL) mediated a significant decrease in the growth rate of amastigote forms of both species. Thymoquinone (CC 50 38.8 mg/mL) exhibited higher cytotoxic effects against murine macrophages than the other extracts. Conclusion: N. sativa, especially its active principle, thymoquinone, showed a potent leishmanicidal activity against L. tropica and L.infantum with an in vitro model.

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