Promising Effects of Rhanterium epapposum L. and Its Main Compounds Alone and Combined with Pyrimethamine Against Toxoplasma gondii Infection

Introduction: Herbs and their products are a source for drug discovery, and most of all synthetic drugs originate from them. The present study was designed to evaluate the in vitro and in vivo efficacy, as well as the potential mechanisms, of Rhanterium epapposum essential oil (REE), β-myrcene (MC), camphene (CP), and limonene (LN) alone and in combination with pyrimethamine (PYM) against Toxoplasma gondii. Materials and Methods: In vitro, the effectiveness of REE and its components on tachyzoites, the infectivity rate, caspase-3 activity, and nitric oxide (NO) and expression levels of inducible NO synthase and gamma interferon (IFN-γ) genes were evaluated. In the in vivo assays, infected mice received REE, MC, CP, and LN either alone or in combination with PYM for 2 weeks. Subsequently, the number and diameter of tissue cysts, oxidant/antioxidant enzyme levels, inflammatory cytokines, and bradyzoite surface antigen 1 (BAG1) gene expression were examined. Results: The best 50% inhibitory concentration values were reported for MC + LN, PYM + MC, and MC + CP, with values of 12.1, 15.4, and 16.6 µg/mL, respectively. REE and its primary compounds significantly increased (p < 0.001) NO release (6.6–14.1 nM), caspase-3 activity, and the expression levels of inducible NO synthase and IFN-γ genes in cells. In addition, significantly decreased (p < 0.001) the number (0.0–115.3 cysts) and size (0.0–83.1 nm) of tissue cysts, oxidative stress markers, decreased the expression levels of IL-1β and TNF-α, and BAG1 (0.48–5.10 fold change), while, significantly increased (p < 0.001) glutathione peroxidase (1.65–5.12 U/mg) and superoxide dismutase (31.9–74.1 U/mg) levels in the infected mice. Conclusions: We demonstrated the high in vitro and in vivo efficacy of REE and its principal compounds against chronic toxoplasmosis. The highest efficacy was observed following combination therapy of T. gondii-infected mice with PYM and these compounds, with a significant difference noted compared with PYM alone. However, further trials must validate these findings and clarify the underlying mechanisms.