Oregano essential oil alone and in combination with biogenic silver nanoparticles exhibits anti-Toxoplasma gondii activity in human trophoblastic cells.

INTRODUCTION: Toxoplasmosis, caused by Toxoplasma gondii, is a globally significant zoonosis, particularly severe in immunocompromised individuals and in ocular and congenital infections. Conventional treatment with pyrimethamine and sulfadiazine is limited by its toxicity, highlighting the need for safer and more effective alternatives. In this context, oregano essential oil (Origanum vulgare L., OEO) and biogenic silver nanoparticles (AgNp-Bio) have emerged as promising candidates due to their vast antiparasitic activity and low toxicity. METHODS: This study evaluated the anti-T. gondii effects and mechanisms of action of OEO, whose major constituents were carvacrol (72%), p-cymene (5%), γ-terpinene (4%) and thymol (2%), alone and in combination with Fusarium oxysporum-biosynthesized AgNp-Bio in an in vitro model of congenital toxoplasmosis using HTR8/SVneo trophoblastic cells. RESULTS: Both treatments displayed low cytotoxicity and strong antiparasitic activity against free and intracellular forms of T. gondii, reducing infection and proliferation rates. OEO demonstrated high selectivity toward the parasite, with selectivity index values of 21.58 for free forms and 7.96 for intracellular forms. The combination of OEO + AgNp-Bio exhibited an additive effect in free tachyzoites (fractional inhibitory concentration index, FICI = 0.62), but an antagonistic effect in intracellular forms (FICI = 6.38). Metabolic analyses revealed increased reactive oxygen species (ROS), mitochondrial membrane depolarization, formation of lipid and autophagic bodies in free tachyzoites, as well as membrane exposure and propidium iodide staining, suggesting late apoptosis-like death. In infected cells, treatments also modulated ROS and nitric oxide production. CONCLUSION: These findings demonstrate the anti-Toxoplasma effect of OEO and the context-dependent effect of its combination with AgNp-Bio, standing out as a promising candidate for further investigation against congenital toxoplasmosis.