Using citrate-functionalized TiO2 nanoparticles to study the effect of particle size on zebrafish embryo toxicity

• Published in: Analyst (London) 2014-03, Vol.139 (5), p.964-972
• Main Authors: Kim, M.-S, Louis, K. M, Pedersen, J. A, Hamers, R. J, Peterson, R. E, Heideman, W
• Format: Article
• Language: English
• Subjects: Animals; Citric Acid - toxicity; Embryonic Development - drug effects; Embryonic Development - physiology; Metal Nanoparticles - toxicity; Oxidative Stress - drug effects; Oxidative Stress - physiology; Particle Size; Reactive Oxygen Species - metabolism; Titanium - toxicity; Zebrafish
• ISSN: 0003-2654; 1364-5528
• DOI: 10.1039/c3an01966g

TiO 2 nanoparticles (NPs) are photoactive, potentially producing toxicity in vivo in the presence of sunlight. We have previously demonstrated photodependent toxicity in zebrafish embryos exposed to TiO 2 NPs. Here we investigate the effect of particle size on developing zebrafish exposed to 6, 12 and 15 nm citrate-functionalized anatase TiO 2 NPs under either simulated sunlight illumination or in the dark. All three sizes of TiO 2 NPs caused photo-dependent toxicity. Under simulated sunlight illumination, the acute toxicity of the 6 nm citrate-TiO 2 NPs (120 h LC 50 of 23.4 mg L −1 ) exceeded that of the 12 and 15 nm citrate-TiO 2 NPs. Exposure to 6 nm particles under illumination also caused a higher incidence of developmental defects than the larger particles. These abnormalities included pericardial edema, yolk-sac edema, craniofacial malformation, and opaque yolk. To gain insight into the mechanisms of toxicity, we measured hydroxyl radicals (&z.rad;OH) generated by NPs in vitro and reactive oxygen species (ROS) produced in vivo . We found that on a mass basis, smaller particles generated higher levels of ROS both in vitro and in vivo , and the 6 nm citrate-TiO 2 NPs induced more oxidative stress than larger particles in the zebrafish embryo. We examined oxidative DNA damage by measuring 8-hydroxydeoxyguanosine in zebrafish exposed to different-sized citrate-TiO 2 NPs and found that 6 nm particles caused more DNA damage than did larger particles (12 and 15 nm) under illumination. Our results indicate a photo-dependent toxicity of citrate-TiO 2 NPs to zebrafish embryos, with an inverse relationship between particle size and toxicity. Production of more ROS, resulting in more oxidative stress and more DNA damage, represents one possible mechanism of the higher toxicity of smaller citrate-TiO 2 NPs. These results highlight the relationship between citrate-TiO 2 NP size and toxicity/oxidative stress in developing zebrafish embryos. TiO 2 nanoparticles (NPs) are photoactive, potentially producing toxicity in vivo in the presence of sunlight.