The ROS scavenging and renal protective effects of pH-responsive nitroxide radical-containing nanoparticles.

The ultimate objective of nanoparticle-based therapy is to functionalize nanomedicines in a micro-disease environment without any side effects. Here, we reveal that our pH-responsive nitroxide radical-containing nanoparticles (RNP(pH)) disintegrate within the renal acidic lesion and act as scavengers of reactive oxygen species (ROS), leading to a relief of acute kidney injury (AKI). RNP(pH) was prepared using amphiphilic block copolymers possessing 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) moieties via amine linkage as a side chain of the hydrophobic segment. The self-assembled RNP(pH) disintegrated at pH below 7.0 because of a protonation of the amino groups in the hydrophobic core of the nanoparticles, thereby resulting in an improvement in ROS scavenging activity. Using a renal ischemia-reperfusion AKI model in mice, the therapeutic effect of RNP(pH) on ROS damage was evaluated. Unlike the RNP without pH-triggered disintegration (RNP(Non-pH)), the RNP(pH) showed extremely high ROS scavenging activity and renal protective effects. It is interesting to note that the side effect of nitroxide radicals was markedly suppressed due to the compartmentalization of nitroxide radicals in the core of RNP(pH) in untargeted area. The morphology changes in RNP(pH) were confirmed by analyzing electron spin resonance spectra, and these findings provide the evidence of the real therapeutic effect of the environment-sensitive specific disintegration of nanoparticles in vivo.