The analgesia efficiency of ultrasmall magnetic iron oxide nanoparticles in mice chronic inflammatory pain model.

Few studies have investigated the effects of iron oxide nanoparticles (NPs) on analgesia. We developed inflammatory pain models via complete Freund's adjuvant injection over the hind paw in CD1 mice. Various doses of magnetite (FeO) NPs were injected into the paw. Analgesia behavior was checked with von Frey microfilament and thermal irradiation measurements. Paw skin tissues were harvested at the maximal analgesia time point. The presence of activated white cells (CD68, myeloperoxidase) and free radical (reactive oxygen species, ROS) production was also checked. Western blotting was used to identify the changes of ROS production enzymes. FeO NPs demonstrated a dose-related analgesia effect with significant reduction in inflammatory cells, pro-inflammatory markers, and ROS production in the lesion paw. ROS production enzyme expression also declined. The results indicate that local FeO NP administration induced significant analgesia via attenuation of inflammatory cell infiltration and pro-inflammatory signaling as well as scavenging of microenvironment free radicals in a mouse inflammatory pain model.