Effect of nitric oxide on acanthamoeba castellanii

PURPOSE. Acanthamoeba keratitis is a well-known intractable corneal infectious disease. We investigated the anti-Acanthamoeba effect of exogenous nitric oxide (NO). METHODS. Acanthamoeba castellanii was axenically cultured and exposed to various concentrations of NO donors, such as sodium nitrite, sodium nitroprusside (SNP), and NO-releasing silica nanoparticles (coated in branched polyethylene imine, size:100 nm), for 1 to 7 days (sodium nitrite and SNP: 0, 0.1, 1, 10, 100, and 1000 μM; silica nanoparticles: 0, 6.25, 12.5, 25, 50, and 100 μg/mL). Human corneal epithelial cells (HCECs) were cultured and exposed to sodium nitrite, SNP (0, 0.1, 1, 10, 100, and 1000 μM), and silica nanoparticles for 1, 2, and 3 days. RESULTS. Sodium nitrite and SNP showed a dose-dependent inhibitory effect on A. castellanii viability. A more prominent inhibitory effect was observed with SNP (less than 10% of organisms survived at 7-day culture with 1000 μM) compared with sodium nitrite. However, more cytotoxicity on HCEC was observed with SNP. NO-releasing silica nanoparticles were successfully internalized into the amoebic cytoplasm and accumulated in large vacuoles. Although blank silica nanoparticles had no inhibitory effect on A. castellanii viability, NO-releasing silica nanoparticles showed a dose-dependent amoebicidal effect. Furthermore, no cystic transformation of A. castellanii was observed under a phase contrast microscope or transmission electron microscope after exogenous NO treatment. CONCLUSIONS. Our results demonstrated the anti-Acanthamoeba effect of exogenous NO. This finding suggests that NO-releasing drug platforms, including nano-carriers, can be a promising therapeutic strategy for Acanthamoeba keratitis.