We studied adult zebrafish to determine whether the size of 20 and 110 nm citrate-coated silver nanoparticles (AgC NPs) differentially impact the gills and intestines, known target organs for Ag toxicity in fish. Following exposure for 4 h, 4 days, or 4 days plus a 7 day depuration period, we obtained different toxicokinetic profiles for different particle sizes, as determined by Ag content of the tissues. Ionic AgNO3 served as a positive control. The gills showed a significantly higher Ag content for the 20 nm particles at 4 h and 4 days than the 110 nm particles, while the values were more similar in the intestines. Both particle types were retained in the intestines even after depuration. These toxicokinetics were accompanied by striking size-dependent differences in the ultrastructural features and histopathology in the target organs in response to the particulates. Ag staining of the gills and intestines confirmed prominent Ag deposition in the basolateral membranes for the 20 nm but not for the 110 nm particles. Furthermore, it was possible to link the site of tissue deposition to disruption of the Na(+)/K(+) ion channel, which is also localized to the basolateral membrane. This was confirmed by a reduction in ATPase activity and immunohistochemical detection of the α subunit of this channel in both target organs, with the 20 nm particles causing significantly higher inhibition and disruption than the larger size particles or AgNO3. These results demonstrate the importance of particle size in determining the hazardous impact of AgNPs in the gills and intestines of adult zebrafish.

Manufactured metal (oxide) nanoparticles are entering the aquatic environment with little understanding on their potential health impacts for exposed organisms. Adopting an integrative approach, we investigated effects of particle size and coating on biological responses for two of the most commonly used metal (oxide) nanoscale particles, silver (Ag) and titanium dioxide (TiO₂) in zebrafish embryos. Titanium dioxide nanoparticles (nominally, 4 nm, 10 nm, 30 nm and 134 nm) had little or no toxicity on the endpoints measured. Ag both in nano form (10 nm and 35 nm) and its larger counterpart (600-1600 nm) induced dose-dependent lethality and morphological defects, occurring predominantly during gastrula stage. Of the silver material tested 10 nm nanoparticles appeared to be the most toxic. Coating Ag nanoparticles with citrate or fulvic acid decreased toxicity significantly. In situ hybridisation analysis identified the yolk syncytial layer (YSL) as a target tissue for Ag-nano toxicity where there was a significant induction of the heavy metal stress response gene, metallothionein 2 (Mt2) at sub-lethal exposures. Coherent Anti-stroke Raman Scattering (CARS) microscopy provided no evidence for silver particles crossing the chorionic membrane in exposed embryos. Collectively, our data suggest that silver ions play a major role in the toxicity of Ag nanoparticles.

Recent studies suggest that the nanorods consisting of europium hydroxide could promote angiogenesis. In this study, we sought to determine if additional types of nanoparticles were capable of enhancing angiogenesis and in addition, understand the underlying mechanisms. For this reason, we employed a method that combines a high throughput in vitro cell based screen coupled with an in vivo validation using vascular specific green fluorescent protein (GFP) reporter transgenic zebrafish for examining proangiogenesis activity. After screening multiple types of nanoparticles, we discovered that four of them: EuIII(OH)3 rods (Eu Rods), EuIII(OH)3 spheres (Eu Spheres), TbIII(OH)3 rods (Tb Rods) and TbIII(OH)3 spheres (Tb Spheres), were the most effective in promoting angiogenesis. We also showed that ionic forms of europium nitrate [Eu(NO3)3] (Eu) and terbium nitrate [Tb(NO3)3] (Tb), the two lanthanide elements for these four nanoparticles, were also capable of enhancing angiogenesis. However, this effect was further enhanced by nanoparticle synthesis. Finally, we demonstrated that reactive oxygen species H2O2 is a key factor in the process of proangiogenesis by lanthanide elemental nanoparticles.