Efficacy of Black Seed Oil from Nigella sativa against Murine Infection with Cysts of Me49 Strain of Toxoplasma gondii

Background: New therapies for toxoplasmosis are critically needed. Nigella sativa, commonly known as black seed or black cumin, has been known to include many medicinal properties. It has anti-inflammatory, and immuno-potentiating effects, antihelminthic and antiprotozoal activities. Objective: To study the effect of black seed oil (BSO) from Nigella sativa against Toxoplasma gondii Me49 strain in a murine model of infection. Materials and Methods: Two separate studies were performed, in which mice were orally inoculated with 10 or 20 T. gondii (Me49 strain) brain cysts. In each study, three groups of mice (35 each) were assigned to treatment with BSO for 2 weeks before T. gondii infection (BSO prophylactic), day 4 post infection (BSO therapeutic), or left untreated (infected untreated control). The BSO effect on toxoplasmosis was evaluated by the assessment of (1) survival rate and brain cyst burden, (2) brain histopathological lesions and (3) immunohistochemical expression of inducible nitric oxide synthase (iNOS). Results: In infection induced by inoculation of 10, but not 20, cysts/mouse of the Me49 strain, BSO in prophylactic or therapeutic regimens significantly enhanced protection of infected mice against death (P = 0.01) and reduced brain cyst burdens at 5, 7 and 12 weeks post infection (PI) (P < 0.05) compared to the infected untreated control. The brains of BSO prophylactic or therapeutic groups showed milder meningitis, encephalitis and perivascular cuffing compared to the infected untreated control (P < 0.05). Moreover, expression of iNOS was significantly enhanced in both BSO prophylactic and therapeutic groups compared to the untreated infected control. The BSO prophylactic group showed a significant enhanced expression of iNOS, selective to the brain endothelial cells, in the 1st week PI. Infection with 20 cysts was more aggressive, resulting in death of all untreated mice by day 35, and 26.7% and 20% protection respectively in BSO prophylactic and therapeutic groups. The estimated probabilities of survival were not significantly different among the 3 groups (P = 0.112). Conclusion: BSO showed promising prophylactic and therapeutic effects on murine toxoplasmosis. Recommendations: Further studies are needed to test the anti-Toxoplasma effect of N. sativa constituents. Additionally, further research work is required to study its prophylactic efficacy against reactivated toxoplasmosis.