Abstract
The present study examined the potential toxic concentrations of zinc oxide nanoparticles (ZnO NPs) and associated autophagy and apoptosis-related injuries in primary neocortical astrocyte cultures. Concentrations of ZnO NPs ≥3 μg/mL induced significant toxicity in the astrocytes. At 24 h after exposure to the ZnO NPs, transmission electron microscopy revealed swelling of the endoplasmic reticulum (ER) and increased numbers of autophagolysosomes in the cultured astrocytes, and increased levels of LC3 (microtubule-associated protein 1 light chain 3)-mediated autophagy were identified by flow cytometry. Apoptosis induced by ZnO NP exposure was confirmed by the elevation of caspase-3/7 activity and 4′,6′-diamidino-2-phenylindole (DAPI) staining. Significant (p < 0.05) changes in the levels of glutathione peroxidase, superoxide dismutase, tumor necrosis factor (TNF-α), and interleukin-6 were observed by enzyme-linked immunoassay (ELISA) assay following the exposure of astrocyte cultures to ZnO NPs. Phosphatidylinositol 3-kinase (PI3K)/mitogen-activated protein kinase (MAPK) dual activation was induced by ZnO NPs in a dose-dependent manner. Additionally, the Akt (protein kinase B) inhibitor BML257 and the mTOR (mammalian target of rapamycin) inhibitor rapamycin contributed to the survival of astrocytes. Inhibitors of cyclooxygenase-2 and lipoxygenase attenuated ZnO NP-induced toxicity. Calcium-modulating compounds, antioxidants, and zinc/iron chelators also decreased ZnO NP-induced toxicity. Together, these results suggest that ZnO NP-induced autophagy and apoptosis may be associated with oxidative stress and the inflammatory process in primary astrocyte cultures.
Highlights
Zinc oxide nanoparticles (ZnO NPs) have been widely used for medicinal purposes, such as photodynamic therapy [1] and piezoelectric nanomaterials for biomedical applications [2,3,4], various consumer products such as cosmetics and food additives, and industrial materials such as plastics, paints, and ceramics [5,6]
ZnO NPs have some positive medical applications due to their antibacterial and anticancer effects, brain injury may occur at any time in both human and non-human biological systems because these nanoparticles can break down the blood–brain barrier (BBB) or be uptaken via olfactory sensory neurons in the nose following prolonged exposure or overdose [8,9,10]
Using transmission electron microscopy (TEM), we confirmed that autophagolysosome formation and endoplasmic reticulum (ER) swelling were evident following treatment with ZnO NPs. These results suggest that ZnO NPs may induce the production of pro-inflammatory cytokines, such as IL-6 and tumor necrosis factor (TNF)-α, via activation of the ER stress–autophagy axis [42]
Summary
Zinc oxide nanoparticles (ZnO NPs) have been widely used for medicinal purposes, such as photodynamic therapy [1] and piezoelectric nanomaterials for biomedical applications [2,3,4], various consumer products such as cosmetics and food additives, and industrial materials such as plastics, paints, and ceramics [5,6]. The number of apoptosis and autophagy studies using ZnO NPs is increasing, few reports have investigated ZnO NP-related toxicity in astrocytes, which are glial cells that play important roles in the CNS [19,25]. In this study, we investigated (1) significant toxic concentrations of ZnO NPs; (2) astrocyte morphology using transmission electron microscopy (TEM) and mean autophagy intensity using the LC3 (microtubule-associated protein 1 light chain 3) antibody; (3) caspase-3/7 activity and nuclear fluorescence staining; (4) the pro-inflammatory cytokines IL-6 and TNF-α, and antioxidant enzymes SOD and GPx; (5) PI3K/MAPK activation; and (6) the protective effects of various chemicals, such as COX-2/LOX, PI3K, Akt (protein kinase B), and mTOR (mammalian target of rapamycin) inhibitors, calcium modulators, antioxidants, and zinc/iron chelators that might protect astrocytes from ZnO NP-induced injury
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
