Zinc oxide nanoparticles (ZnO NPs) have been widely used in cosmetics and sunscreens, advanced textiles, self-charging and electronic devices; the potential for human exposure and the health impact at each stage of their manufacture and use are attracting great concerns. In addition to pulmonary damage, nanoparticle exposure is also strongly correlated with the increase in incidences of cardiovascular diseases; however, their toxic potential remains largely unclear. Herein, we investigated the cellular responses and endoplasmatic reticulum (ER) stress induced by ZnO NPs in human umbilical vein endothelial cells (HUVECs) in comparison with the Zn2+ ions and CeO2 NPs. We found that the dissolved zinc ion was the most significant factor for cytotoxicity in HUVECs. More importantly, ZnO NPs at noncytotoxic concentration, but not CeO2 NPs, can induce significant cellular ER stress response with higher expression of spliced xbp-1, chop, and caspase-12 at the mRNA level, and associated ER marker proteins including BiP, Chop, GADD34, p-PERK, p-eIF2α, and cleaved Caspase-12 at the protein levels. Moreover, ER stress was widely activated after treatment with ZnO NPs, while six of 84 marker genes significantly increased. ER stress response is a sensitive marker for checking the interruption of ER homeostasis by ZnO NPs. Furthermore, higher dosage of ZnO NPs (240 μM) quickly rendered ER stress response before inducing apoptosis. These results demonstrate that ZnO NPs activate ER stress-responsive pathway and the ER stress response might be used as an earlier and sensitive end point for nanotoxicological study.

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The environmental pollution associated with electrical discharge machining is not yet clearly understood. Airborne exposure to nanoscale and respirable particles were investigated with regard to the aerosol characteristics of a wire electrical discharge machining (WEDM) workshop. The total number concentration of the aerosol was multimodal, with the highest peak maxima during the working hours of 10:00 am and 3:00 pm. The majority of the released particles were smaller than d = 100 nm, with the maximum amount sized 40 nm. A large quantity of metallic elements, including Fe, Al and Cu, were found in the aerosol particulates coming from WEDM processing. Furthermore, the aerosol particles exhibited higher cellular toxicity and ROS producing ability in human alveolar epithelial cells (16HBE) when compared to the atmospheric background. Our results indicate substantial hazards arising from exposure to polluted atmosphere of a WEDM workshop. Effective exposure controls and protections are thus strongly recommended.

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