Abstract
Toxoplasma gondii is an intracellular parasitic protozoan with a high infection rate in mammals, including humans, and birds. There is no effective vaccine, and treatment relies on antiparasitic drugs. However, existing antiprotozoal drugs have strong side effects and other problems; therefore, new treatment approaches are needed. Metal nanoparticles have attracted increased interest in the biomedical community in recent years because of their extremely high surface area to volume ratio and their unique reactivity that could be exploited for medicinal purposes. Previously, we confirmed the anti-Toxoplasma effects of gold, silver, and platinum nanoparticles, in a growth inhibition test. Here, we asked whether the anti-Toxoplasma effect could be confirmed with less expensive metal nanoparticles, specifically iron oxide nanoparticles (goethite and hematite). To improve the selective action of the nanoparticles, we modified the surface with l-tryptophan as our previous findings showed that the bio-modification of nanoparticles enhances their selectivity against T. gondii. Fourier-Transform Infrared Spectroscopy (FTIR) analysis confirmed the successful coating of the iron oxide nanoparticles with l-tryptophan. Subsequently, cytotoxicity and growth inhibition assays were performed. L-tryptophan-modified nanoparticles showed superior anti-Toxoplasma action compared to their naked nanoparticle counterparts. L-tryptophan enhanced the selective toxicity of the iron oxide nanoparticles toward T. gondii. The bio-modified nanoparticles did not exhibit detectable host cell toxicity in the effective anti-Toxoplasma doses. To elucidate whether reactive oxygen species contribute to the anti-Toxoplasma action of the bio-modified nanoparticles, we added Trolox antioxidant to the assay medium and found that Trolox appreciably reduced the nanoparticle-induced growth inhibition.