Responses of Caenorhabditis elegans to various surface modifications of alumina nanoparticles.

The surface modifications of nanoparticles (NPs), are well-recognized parameters that affect the toxicity, while there has no study on toxicity of Al2O3 NPs with different surface modification. Therefore, for the first time, this study pays attention to evaluating the toxicity and potential mechanism of pristine Al2O3 NPs (p-Al2O3), hydrophilic (w-Al2O3) and lipophilic (o-Al2O3) modifications of Al2O3 NPs both in vitro and in vivo. Applied concentrations of 10, 20, 40, 80,100 and 200 μg/mL for 24 h exposure on Caenorhabditis elegans (C. elegans), while 100 μg/mL of Al2O3 NPs significantly decreased the survival rate. Using multiple toxicological endpoints, we found that o-Al2O3 NPs (100 μg/mL) could induce more severe toxicity than p-Al2O3 and w-Al2O3 NPs. After uptake by C. elegans, o-Al2O3 NPs increased the intestinal permeability, easily swallow and further destroy the intestinal membrane cells. Besides, cytotoxicity evaluation revealed that o-Al2O3 NPs (100 μg/mL) are more toxic than p-Al2O3 and w-Al2O3. Once inside the cell, o-Al2O3 NPs could attack mitochondria and induce the over-production of reactive oxygen species (ROS), which destroy the intracellular redox balance and lead to apoptosis. Furthermore, the transcriptome sequencing and RT-qPCR data also demonstrated that the toxicity of o-Al2O3 NPs is highly related to the damage of cell membrane and the imbalance of intracellular redox. Generally, our study has offered a comprehensive sight to the adverse effects of different surface modifications of Al2O3 NPs on environmental organisms and the possible underlying mechanisms.