Effect of Thymoquinone on <i>Toxoplasma gondii’s</i> Tachyzoite Form

Background: Pyrimethamine and sulfadiazine, while being effective against toxoplasmosis, are limited by significant adverse effects. On the other hand, 2-isopropyl-5-methyl-1,4-benzoquinone has been identified as a key bioactive compound. Moreover, studies on thymoquinone (TQ) have demonstrated its cytotoxic activity, inhibiting the growth of various cancer cell lines, including those of the ovary, prostate, colon, pancreas, osteosarcoma, and breast, as well as leukemia cells. This study sought to determine how TQ affected the tachyzoite type of Toxoplasma gondii. Materials and Methods: Different TQ concentrations (6.25–400 µM) were prepared in microtiter plates for this experiment. The tachyzoite test was used to assess parasite mortality. Flow cytometry was performed to determine whether T. gondii tachyzoites underwent apoptosis. Specifically, 2×10^5 tachyzoites were exposed to TQ at concentrations of 50 µM, 100 µM, and 200 µM, following the kit’s instructions. Results: Light microscopy revealed that TQ had lethal and damaging effects on T. gondii. Based on 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT) assays, 400 µM of TQ exhibited the most toxic effects on macrophages. Furthermore, the MTT assay determined a half-maximal inhibitory concentration (CC50 ) for macrophages. Flow cytometric analysis indicated that the percentages of total apoptosis in parasites exposed to 50 µM, 100 µM, and 200 µM TQ were 51.3%, 64.9%, and 70.8%, respectively. Conclusion: The results demonstrated that TQ is toxic to T. gondii and induces apoptosis in this parasite. This work provides supporting evidence for the use of TQ in antiparasitic assays.