Behavioral Impairments and Oxidative Stress in the Brain, Muscle, and Gill Caused by Chronic Exposure of C70 Nanoparticles on Adult Zebrafish

There is an imperative need to develop efficient whole-animal-based testing assays to determine the potential toxicity of engineered nanomaterials. While previous studies have demonstrated toxicity in lung and skin cells after C-70 nanoparticles (NPs) exposure, the potential detrimental role of C-70 NPs in neurobehavior is largely unaddressed. Here, we evaluated the chronic effects of C-70 NPs exposure on behavior and alterations in biochemical responses in adult zebrafish. Two different exposure doses were used for this experiment: low dose (0.5 ppm) and high dose (1.5 ppm). Behavioral tests were performed after two weeks of exposure of C-70 NPs. We found decreased locomotion, exploration, mirror biting, social interaction, and shoaling activities, as well as anxiety elevation and circadian rhythm locomotor activity impairment after 2 weeks in the C-70 NP-exposed fish. The results of biochemical assays reveal that following exposure of zebrafish to 1.5 ppm of C-70 NPs, the activity of superoxide dismutase (SOD) in the brain and muscle tissues increased significantly. In addition, the concentration of reactive oxygen species (ROS) also increased from 2.95 +/- 0.12 U/ug to 8.46 +/- 0.25 U/ug and from 0.90 +/- 0.03 U/ug to 3.53 +/- 0.64 U/ug in the muscle and brain tissues, respectively. Furthermore, an increased level of cortisol was also observed in muscle and brain tissues, ranging from 17.95 +/- 0.90 pg/ug to 23.95 +/- 0.66 pg/ug and from 3.47 +/- 0.13 pg/ug to 4.91 +/- 0.51 pg/ug, respectively. Increment of Hif1-alpha level was also observed in both tissues. The elevation was ranging from 11.65 +/- 0.54 pg/ug to 18.45 +/- 1.00 pg/ug in the muscle tissue and from 4.26 +/- 0.11 pg/ug to 6.86 +/- 0.37 pg/ug in the brain tissue. Moreover, the content of DNA damage and inflammatory markers such as ssDNA, TNF-alpha, and IL-1 beta were also increased substantially in the brain tissues. Significant changes in several biomarker levels, including catalase and malondialdehyde (MDA), were also observed in the gill tissues. Finally, we used a neurophenomic approach with a particular focus on environmental influences, which can also be easily adapted for other aquatic fish species, to assess the toxicity of metal and carbon-based nanoparticles. In summary, this is the first study to illustrate the adult zebrafish toxicity and the alterations in several neurobehavior parameters after zebrafish exposure to environmentally relevant amounts of C-70 NPs.