Original Contribution
Titanium dioxide nanoparticles induce strong oxidative stress and mitochondrial damage in glial cells

https://doi.org/10.1016/j.freeradbiomed.2014.04.026Get rights and content

Highlights

  • Titanium dioxide nanoparticles (TiO2 NPs) induced oxidative stress in glial cells.

  • TiO2 NPs induced mitochondrial damage.

  • TiO2 NPs could induce cerebral damage and neurodegenerative diseases.

Abstract

Titanium dioxide nanoparticles (TiO2 NPs) are widely used in the chemical, electrical, and electronic industries. TiO2 NPs can enter directly into the brain through the olfactory bulb and can be deposited in the hippocampus region; therefore, we determined the toxic effect of TiO2 NPs on rat and human glial cells, C6 and U373, respectively. We evaluated some events related to oxidative stress: (1) redox-signaling mechanisms by oxidation of 2′,7′-dichlorodihydrofluorescein diacetate; (2) peroxidation of lipids by cis-parinaric acid; (3) antioxidant enzyme expression by PCR in real time; and (4) mitochondrial damage by MitoTracker Green FM staining and Rh123. TiO2 NPs induced a strong oxidative stress in both glial cell lines by mediating changes in the cellular redox state and lipid peroxidation associated with a rise in the expression of glutathione peroxidase, catalase, and superoxide dismutase 2. TiO2 NPs also produced morphological changes, damage of mitochondria, and an increase in mitochondrial membrane potential, indicating toxicity. TiO2 NPs had a cytotoxic effect on glial cells; however, more in vitro and in vivo studies are required to ascertain that exposure to TiO2 NPs can cause brain injury and be hazardous to health.

Section snippets

Materials

Dulbecco׳s modified Eagle׳s medium (DMEM), antibiotic–antimycotic 100× solution, minimal essential medium (MEM) nonessential amino acids and pyruvate solutions (100×), 0.25% trypsin–EDTA solution, and newborn calf serum (NBCS) were purchased from Gibco/BRL (Grand Island, NY, USA). Sterile plastic material for tissue culture was from Corning (Corning, NY, USA). Flow cytometry reagents were purchased from Becton–Dickinson Immunocytometry Systems (San Jose, CA, USA).

TiO2 NPs induced oxidative stress

To determine if TiO2 NPs could induce damage in glial cells, we determined the changes in the cellular redox state caused by oxidative stress mediating the oxidation of H2DCFDA. TiO2 NPs induced a strong increase in H2DCFDA oxidation in C6 and U373 cells, in comparison with the negative control (Fig. 1). This rise was observed from 2 h after treatment, with a maximal increase at 6 h and a decrease at 24 h in both cell lines.

Considering that TiO2 NPs induce a strong oxidative stress, the expression

Discussion

Because TiO2 NPs can translocate into the CNS, we evaluated their possible toxic effect on glial cells, which are the principal component of the CNS and provide support and protection to neurons. Several toxicity studies on astrocytes (astrocytic glial cells or astroglia) using cultures of primary, subcultured, or permanent cell lines (astrocytomas), have been extremely valuable in toxicity evaluation and to understand the mechanisms of action of a number of neurotoxic substances [32];

Conclusions

In conclusion, TiO2 NPs induced a strong oxidative stress, mediated by change in the redox state as well as by a decrease in genes of antioxidant enzymes, lipid peroxidation, reduction in mitochondrial membrane potential, and mitochondrial depolarization, in glial cells in vitro. These findings suggest that the exposure of brain cells in vivo to TiO2 NPs could cause brain injury, contribute to the development of neurodegenerative diseases [58], and be hazardous to health.

Acknowledgments

We thank to CONACyT, for providing financial support to Elizabeth Huerta-García, Sandra Gissela Márquez-Ramírez, and José Antonio Pérez-Arizti, graduate students from the Posgrado en Investigación en Medicina, Escuela Superior de Medicina, Instituto Politécnico Nacional and from the Posgrado en Ciencias Biológicas, Universidad Nacional Autónoma de México, Scholarship Nos. 227281, 175962, and 294521, respectively. We also thank CONACyT for economical support of this work and Project 182341.

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    These authors contributed equally to this work.

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