Ferrihydrite Nanoparticles Alleviate Rheumatoid Arthritis by Nanocatalytic Antioxidation and Oxygenation.

Oxidative stress and hypoxia are two key biochemical factors in the development of rheumatoid arthritis (RA). As both reactive oxygen species (ROS) and oxygen gas (O 2 ) are oxygen-related chemicals, we suggest that a redox reaction converting ROS into O 2 can mitigate oxidative stress and hypoxia concurrently, synergistically modulating the inflammatory microenvironment. In this work, ferrihydrite, a typical iron oxyhydroxide, is prepared in nanodimensions in which tetrahedrally coordinated Fe can form a composite catalytic center by coupling with an adjacent hydroxyl group, cooperatively facilitating H 2 O 2 decomposition and O 2 generation, presenting a high catalase-like activity. In the RA region, the nanomaterial catalyzes the conversion of excess H 2 O 2 into O 2 , achieving both antioxidation and oxygenation favoring the alleviation of inflammation. Both cellular and in vivo experiments demonstrate the desirable efficacy of ferrihydrite nanoparticles for RA treatment. This work provides a methodology for the catalytic therapy of inflammatory diseases featuring both oxidative stress and hypoxia.