Evaluation of the Toxicity and Antioxidant Activity of Redox Nanoparticles in Zebrafish (Danio rerio) Embryos

Recently, we have been developing polymer and nanoparticle-based antioxidative nanotherapeutics. Our strategy is to eliminate overproduced reactive oxygen species (ROS), which are strongly related to various diseases. In order to facilitate the transition of the nanotherapeutics into clinical studies, we investigated the toxicity and antioxidant activity of our nanoparticles in a zebrafish model. In this study, zebrafish larvae were exposed to our highly ROS-scavenging nanoparticle (RNP(O)), which was prepared using our original amphiphilic block copolymer, methoxy-poly(ethylene glycol)-b-poly[4-(2,2,6,6-tetramethylpiperidine-1-oxyl)oxymethylstyrene] (MeO-PEG-b-PMOT). When the larvae were exposed to 10-30 mM of low-molecular-weight (LMW) nitroxide radical (4-hydroxyl-2,2,6,6-tetramethylpiperidine-1-oxyl; TEMPOL), all were dead after 12 h, whereas no larva death was observed after exposure to RNP(O) at the same high concentrations. By staining mitochondria from the larvae, we found that LMW TEMPOL significantly induced mitochondrial dysfunction. In contrast, RNP(O) did not cause any significant reduction in the mitochondrial function of zebrafish larvae. It is important to reaffirm that RNP(O) treatment significantly enhanced survival of larvae treated with ROS inducers, confirming the antioxidant activity of RNP(O). Interestingly, RNP(O) exposure induced the expression of Nrf2 target gene (gstp1) in the larvae's intestines and livers. The results obtained in this study indicate that the antioxidative nanoparticle RNP(O) has great potential for clinical trials as it exhibits a potent therapeutic effect and extremely low toxicity to zebrafish embryos.