The fate and oxidative stress of different sized SiO₂ nanoparticles in zebrafish (Danio rerio) larvae

Highlights

• SiO₂ nanoparticles induced oxidative stress in zebrafish larvae.

• ROS levels, antioxidant system and some genes related to oxidative stress were examined.

• Small sized nano-SiO₂ caused more severe oxidative damage to zebrafish larvae.

Abstract

Nanoparticle such as silicon dioxide nanoparticles (nano-SiO₂) are extensively produced and applied in society. Hence there is an increasing concern about their exposure and toxicity to human and wildlife. To understand the effects of sizes of NPs on their bioavailability and toxicity, zebrafish (Danio rerio) embryos (2 h post-fertilization, hpf) were exposed to 25, 50 and 100 mg/L of 15 or 30 nm nano-SiO₂ for 5 days respectively. The results showed that SiO₂ could be readily uptaken by zebrafish, and the accumulation of SiO₂ was significantly higher in 15 nm treatments groups compared to 30 nm nano-SiO₂ treated groups. Furthermore, exposure to 15 nm nano-SiO₂ at the concentration of 100 mg/L resulted in more significant changes in reactive oxygen species (ROS) levels, perturbation of lipid peroxidative and antioxidant system than the same concentration of 30 nm nano-SiO₂, indicating small sized nano-SiO₂ evoked severer oxidative stress in zebrafish larvae. In addition, the more significant up-regulation of transcription of genes related to oxidative stress (e.g., nrf2 and sod1) in 15 nm nano-SiO₂ at the 100 mg/L treatments groups provided more evidence for this speculation. Given the above, 15 nm nano-SiO₂ were more likely to enter and accumulate in zebrafish larvae, thus causing more serious oxidative stress in vivo. These results may provide additional information on the fate and toxicities of different sizes of NPs.

Introduction

Nanoparticles (NPs) are defined as small objects that range in size between 1 and 100 nm. Due to their magnetic, electrical, chemical, mechanical, and optical properties, nanoparticles are widely used. As one common type of nanoparticles, nano-silicon dioxide (nano-SiO₂) are among the top five nanoparticles used in a wide range of applications, including cosmetic development, drug and disease diagnosis (Douroumis et al., 2013, Tang and Cheng, 2013). Recently, individual consumer intake of silica from food was estimated at 9.4 mg/kg bw/day, of which about 1.8 mg/kg bw/day was estimated to be in the nano-size range (Dekkers et al., 2011). Thus, with the increasingly extensive employment of nano-SiO₂, it raises a great concern about the potential effects of nano-SiO₂ on terrestrial and aquatic organisms when it is discharged into the environment (Fent et al., 2010, Duan et al., 2013).

Previous studies have reported the toxic effects of nano-SiO₂ to different animal species, especially to the fish. For example, many hematological parameters were altered after 1 and 25 mg/L nano-SiO₂ exposure to Labeo rohita for 96 h, and plasma electrolytes such as plasma sodium, potassium and chloride levels and Na⁺/K⁺ ATPase activity in gill were all altered, indicating the toxicity of nano-SiO₂ may relate to physiological stress system (Priya et al., 2015). Ramesh et al. (2013) reported that 7-day exposure to nano-SiO₂ resulted in fragmented tissues DNA, and altered activities of antioxidant enzymes including catalase, superoxide dismutase, glutathione-S-transferase, glutathione reductase and GSH in zebrafish (Ramesh et al., 2013). In addition, many studies have demonstrated the size of NPs could be a key factor influencing their bioavailability and toxicity in organisms (Midander et al., 2009). Li et al. (2014) indicated that adult zebrafish showed more significant changes in advanced cognitive neurobehavioral patterns and potentially Parkinson’s disease-like behavior in smaller size (15 nm) nano-SiO₂ exposed groups (Li et al., 2014). In another study, Ye et al. (2010) treated human hepatic cell line with three sizes of nano-SiO₂ (21, 48 and 86 nm) at the concentration from 0.2 to 0.6 mg/mL, the results indicated that nano-SiO₂ caused cytotoxicity dependent on size, dose and time, and only the 21 nm nano-SiO₂ treatment could induce oxidative stress and apoptosis in hepatic cells (Ye et al., 2010). Although it had demonstrated that oxidative stress played an important role in the mechanisms of toxicity of several nanoparticles including nano-SiO₂ (Singh et al., 2009, Ahamed et al., 2010, Wise et al., 2010), studies on oxidative stress toxicity of different sized nano-SiO₂ in fish remain unclear.

To further understand the exact effect of particle size on the fate and toxicology (i.e. oxidative damage) of nano-SiO₂, early staged zebrafish (Danio rerio) were exposed to two sizes of nano-SiO₂ (15 and 30 nm) at a series of concentrations (0, 25, 50 and 100 mg/L). The contents of SiO₂ were measured in exposure water as well as in zebrafish larvae, and ROS levels and several parameters related to oxidative damage were also determined. The results may provide additional information on the fate and toxicities of different sizes of NPs.