The effects of endoplasmic reticulum stress inducer thapsigargin on the toxicity of ZnO or TiO₂ nanoparticles to human endothelial cells

Abstract

It was recently shown that ZnO nanoparticles (NPs) could induce endoplasmic reticulum (ER) stress in human umbilical vein endothelial cells (HUVECs). If ER stress is associated the toxicity of ZnO NPs, the presence of ER stress inducer thapsigargin (TG) should alter the response of HUVECs to ZnO NP exposure. In this study, we addressed this issue by assessing cytotoxicity, oxidative stress and inflammatory responses in ZnO NP exposed HUVECs with or without the presence of TG. Moreover, TiO₂ NPs were used to compare the effects. Exposure to 32 μg/mL ZnO NPs (p < 0.05), but not TiO₂ NPs (p > 0.05), significantly induced cytotoxicity as assessed by WST-1 and neutral red uptake assay, as well as intracellular ROS. ZnO NPs dose-dependently increased the accumulation of intracellular Zn ions, and ZnSO₄ induced similar cytotoxic effects as ZnO NPs, which indicated a role of Zn ions. The release of inflammatory proteins tumor necrosis factor α (TNFα) and interleukin-6 (IL-6) or the adhesion of THP-1 monocytes to HUVECs was not significantly affected by ZnO or TiO₂ NP exposure (p > 0.05). The presence of 250 nM TG significantly induced cytotoxicity, release of IL-6 and THP-1 monocyte adhesion (p < 0.01), but did not significantly affect intracellular ROS or release of TNFα (p > 0.05). ANOVA analysis indicated no interaction between exposure to ZnO NPs and the presence of TG on almost all the endpoints (p > 0.05) except neutral red uptake assay (p < 0.01). We concluded ER stress is probably not associated with ZnO NP exposure induced oxidative stress and inflammatory responses in HUVECs.

Keywords:

• ZnO nanoparticles
• TiO₂ nanoparticles
• human umbilical vein endothelial cells
• thapsigargin
• endoplasmic reticulum stress

Acknowledgements

We appreciate Dr. Peter Moller (University of Copenhagen) to kindly provide the ZnO (NM110) and TiO₂ NPs (NM101) to us.

Disclosure statement

The authors declare no conflict of interest.

Additional information

Funding

This work was financially supported by The Scientific Research Fund of Hunan Provincial Education Department [16C1551], Xiangtan University grant [15XZX19] and Xiangtan University startup grant [15QDZ47].