Abstract
Cerium oxide nanoparticles, also known as nanoceria, possess antioxidative and anti-inflammatory activities in animal models of inflammatory disorders, such as sepsis. However, it remains unclear how nanoceria affect cellular superoxide fluxes in macrophages, a critical type of cells involved in inflammatory disorders. Using human ML-1 cell-derived macrophages, we showed that nanoceria at 1-100 μg/ml potently reduced superoxide flux from the mitochondrial electron transport chain (METC) in a concentration-dependent manner. The inhibitory effects of nanoceria were also shown in succinate-driven mitochondria isolated from the macrophages. Furthermore, nanoceria markedly mitigated the total intracellular superoxide flux in the macrophages. These data suggest that nanoceria could readily cross the plasma membrane and enter the mitochondrial compartment, reducing intracellular superoxide fluxes in unstimulated macrophages. In macrophages undergoing respiratory burst, nanoceria also strongly reduced superoxide flux from the activated macrophage plasma membrane NADPH oxidase (NOX) in a concentration-dependent manner. Token together, the results of the present study demonstrate that nanoceria can effectively diminish superoxide fluxes from both METC and NOX in human macrophages, which may have important implications for nanoceria-mediated protection against inflammatory disease processes.